In a cost plus contract which Larry has mentioned it is a moot point. In those contracts there are re-estimates and scheduled intervals for every phase for the entire life of the project. Those estimates ar go no go points. You and the client either agree to the adjusted budget or you do not. period. In "fixed costs" projects. The procedure is very much the same except that the original estimate is based on the quality of the proposal documents given to the bidder. The estimate can have a range of anywhere from plus/minus 5% up to 25%. Let's say the project is awarded at 1 billion +/- 25%. Once again production check estimates are scheduled and contingency funds are released as adjusted budgets. HOWEVER; during the course of the project there are many client changes that impact either engineering, procurement or construction and cause an unbudgeted cost to the company, For these matters Engineering change notices or field change notices are issued and signed off by the in house client reps as approved. These are NOT reconciled until the plant being built is commissioned and they often add up to millions of dollars. Those are legitimate receivables but are not incorporated into the individual project budgets but are booked as revenue to the company. There are some that the home office clients challenge but very few. Those change orders may not be actually paid for 2 years but they are approved and bookable revenue offset by Halliburton's having to pay the project personnel man-hours out of its own pocket.
The other fly in the ointment is that the scale of projects that Halliburton deals with are many times funded by governments that are very reluctant and sometimes unable to keep cash flow high enough to make some payment schedules so the change orders are booked as IOUs to keep the project budgets coherent. It is risky in one way in that Halliburton is actually short-term financing the project but the set those off with an agreement to take an equity position in the plant being built in case of non-payment.