This paper develops a methodology to assess oil companies managers’ expectations about future oil prices implied in the acquisition of reserves. The method is applied to a sample of farm-ins and farm-outs of onshore developed oil fields in the US from 1979 to 2004, where we make assumptions on expectations on oil production and decline over time. The main findings pointed out that the determinants of the purchase price of reserves has not changed significantly over these 25 years, and that oil companies (or their managers) generally believe in a mean-reverting stochastic process for oil price in the process of bidding and accepting offers for reserves, which means that they expect oil price to increase when it is below historical average, and to decrease when it is above average. We also find that major oil companies are either more conservative than independent firms in estimating future oil prices or strategically decide to focus mainly or large capital-intensive oil prospects.