A process-equipment package can look affordable until the team asks who is paying for its foundations, connecting pipework, power supply and commissioning support. Each item may sit in a different contract. If the interfaces are unclear, an apparently complete EPC budget can still have expensive gaps.
That is where quantity surveying in oil and gas projects becomes useful to an owner. A quantity surveyor (QS) connects the scope being designed, the work being bought and the cost still expected at completion. The owner can then challenge a commitment or change while there is time to act.
This guide covers engineering, procurement and construction (EPC) for oil and gas processing facilities and associated plant works. Exploration and drilling programmes need their own cost structures. The practical examples below are illustrative, not GEMS project results.
Why an EPC contract does not settle the whole budget
EPC brings engineering, procurement and construction into a delivery arrangement. It does not automatically make the owner’s total investment equal to the headline contract price.
Owner-supplied equipment, site investigations, utility connections, specialist support and other retained scope may sit outside that price. Within the contract, qualifications and change provisions affect which party carries a particular cost. Those boundaries need to be understood before an owner treats the budget as committed.
A QS helps make the boundaries visible. Technical teams determine what the plant must do; the commercial review checks whether the scope, quantities, pricing and responsibilities tell the same story.
AACE International’s Total Cost Management Framework connects estimating, planning, forecasting and cost control across a project’s life cycle. Applied to an EPC owner’s decisions, that means keeping one traceable path from the approved scope to the latest forecast, rather than treating the estimate and monthly report as separate exercises.
Put QS support at the decision points
The QS role should change as the project moves forward. Early work tests the budget basis. Later work checks what the owner is buying, paying for and likely to owe.
For the early investment gate, use our guide to checking an oil and gas FEED cost estimate before committing funds.
- Before investment approval: identify gaps in the estimating basis, scope boundaries and allowances.
- Before package award: compare the proposed commitment with the package budget and the complete scope.
- During delivery: review measured progress, payment evidence, changes and the cost to finish.
- At close-out: reconcile the final quantities, agreed changes, outstanding claims and account position.
This does not replace the process engineer, planner, procurement team or contract administrator. The owner should define who prepares information, who verifies it and who approves the commercial decision. A QS needs access to those people and records to provide useful advice.
Break the budget into packages with clear boundaries
A single line for “mechanical works” tells an owner little about a developing overrun. A useful cost breakdown separates the work into packages that can be assigned, measured and reconciled.
Depending on the facility, these might include civil works, structural steel, process equipment, piping, electrical systems, instrumentation and commissioning support. Engineering, construction management, temporary facilities and owner costs also need a defined home.
For each package, record the approved budget, scope inclusions, exclusions, pricing basis and responsible party. Map it to the procurement and finance codes so the same purchase order does not appear in different places in different reports.
Return to the equipment-package example. The equipment supplier’s scope may stop at a defined connection point. The team must establish where connecting services and installation work begin. A scope-responsibility matrix lets the owner see each interface before tender, instead of discovering an unallocated item after award.
The owner’s decision becomes specific: fund the missing work, change the package boundary or resolve the technical requirement before committing.
Keep quantities tied to the design revision
A piping quantity from an early layout and a quantity from coordinated drawings are not interchangeable. Comparing their totals without checking the drawing basis can make design development look like poor site performance.
The measurement record should identify the document revision, measurement rules, units and remaining allowances. Items estimated from factors should be distinguishable from quantities taken from drawings. Equipment lists, piping schedules and cable routes should be reconciled with the relevant package scope.
For process facilities, AACE Recommended Practice 18R-97 relates estimate classification to the maturity of project definition. It also explains that scope maturity alone does not determine an accuracy range; other risks matter. A stage label therefore should not be treated as a guarantee that every quantity is ready for firm pricing.
In a practical QS review, the question is which unresolved quantities could change the next commitment. That directs engineering effort towards commercially significant uncertainty.
Compare the complete purchase, not just the vendor price
Two quotations for a similar item may buy different things. One may include testing, packing and site assistance; another may exclude them. Delivery terms, currency, quote validity and payment milestones can also change the owner’s exposure.
A QS can support procurement by setting out those differences against the package budget. The technical team must first confirm compliance and performance requirements. The commercial comparison then identifies allowances needed to put the offers on a comparable basis.
Keep vendor price, logistics, project-specific duties or taxes and other package costs visible. Use the agreed delivery terms and specialist advice where required; do not assume that one standard percentage covers every purchase.
This review helps the owner decide whether a proposed award fits the full package budget. Detailed long-lead procurement controls deserve a separate review, but this basic check should happen before the order is placed.
Match progress payments to the agreed evidence
Equipment ordered, equipment delivered and equipment installed represent different stages. They should not be counted as the same progress merely because each appears in a contractor’s report.
Start with the contract’s payment mechanism. A milestone contract may require specific documents or acceptance evidence. Measured work may require agreed quantities and rates. Materials held off site may need additional evidence under the contract before payment is appropriate.
The QS can reconcile the application against the schedule of values, previous payments and supporting records. Inspection reports, delivery records and agreed measurement sheets help explain the recommended valuation. Technical acceptance remains with the authorised technical personnel.
For an owner, the benefit is a clearer payment decision and less risk of counting the same work twice. Payment certification and physical progress should also remain distinguishable in the wider project-controls report.
Show change exposure before it becomes an agreed price
A revised routing instruction can affect more than pipe length. It may change supports, access requirements, testing and the installation sequence. The cost effect should be reviewed with engineering and planning before it disappears into several separate claims.
A change register should connect the instruction or event to its scope, estimate, notification status, supporting evidence and approval route. Keep proposed, under-review, agreed and rejected amounts distinct.
A contractor’s submitted amount is not automatically an approved liability. Equally, an unresolved change should not vanish from the forecast just because the parties have not agreed its value. Record the current assessed exposure and the basis used, subject to the contract.
The owner can then see which decisions are overdue, which changes need funding and which records are missing. That is more useful than finding a stack of unresolved submissions at final account.
Forecast the cost to finish without double counting
Low spending early in construction does not prove that a project is under budget. Large orders may already be committed, work may be awaiting valuation, and difficult installation activities may still lie ahead.
The forecast should combine cost already incurred with a current estimate of the remaining work. Finance and project controls need a consistent treatment of accruals, open commitments, unawarded scope and change exposure.
A purchase order that is partly paid must not be added in full to actual costs. Likewise, an allowance for an unresolved change should be reconciled when the change is agreed and enters the commitment record. These are basic checks that keep a plausible-looking forecast from overstating or understating the position.
Risk allowances need the same discipline. Identify what each allowance covers, who owns the risk and whether it is already included elsewhere. Update the position as uncertainty changes. A contingency balance is not permission to approve new scope without review.
Give the owner a report that leads to action
A useful monthly construction cost report should make the next decision easy to find. For an oil and gas EPC project, ask for a package-level view containing:
- the original and current approved budgets, with authorised movements explained;
- commitments, incurred cost and the remaining forecast on a consistent basis;
- agreed changes and assessed unresolved exposure, shown separately;
- forecast final cost against the current budget;
- risk allowances, their movement and any overlap with package forecasts;
- decisions required, named owners and due dates.
Add a short explanation of what changed since the previous report. “Piping forecast increased” is incomplete. The owner needs to know whether the movement came from quantities, rates, productivity, timing or changed scope, and which part can still be influenced.
Agree reporting definitions and a data cut-off with finance and procurement. Without that alignment, teams can debate incompatible totals while the actual commercial decision waits.
When should the owner involve a QS?
Involve the QS while package boundaries and budget assumptions can still be tested. Waiting until a tender exceeds the budget leaves fewer options and usually means revisiting work already done.
Start with the latest scope documents, estimate, procurement plan and responsibility matrix. Agree which decisions need support and what evidence is missing. Then define deliverables and reporting responsibilities proportionate to the project.
The value of QS support is visible in that decision trail: an interface resolved, a quotation clarified, a payment supported or a forecast corrected before the owner acts.
FAQs
Does an oil and gas EPC project need a QS if it has a cost engineer?
It depends on the team’s existing responsibilities. QS work often concentrates on quantities, package commercial reviews, valuations and changes. Cost engineering may cover estimating, forecasting and wider controls. Define the deliverables and interfaces so the roles complement each other without duplicating work.
Does a lump-sum EPC price remove the owner’s cost risk?
No. Retained scope, exclusions, owner changes and other exposures can remain outside the agreed price. The contract determines responsibility. A QS helps the owner identify these items and include an appropriate assessment in the total project forecast.
Can a QS guarantee that the project will stay within budget?
No. A QS can improve the evidence behind budget decisions, identify gaps and report cost exposure. Outcomes still depend on scope decisions, design, market conditions, execution and how the project team responds.
Start with the packages that carry the next commitment
Before approving another award or payment, check that its scope, supporting evidence and forecast treatment agree. If those links are unclear, that is the first review to commission.
