[en] The authors find serious problems in the present tax system when evaluating fields with uncertain income. The tax system is not neutral. This result will depend on the profitability of the project in question, the level of the company's activity and the stochastic representation of price. To circumvent these problems the authors investigate various changes in the tax system. A simple rule where 10% of the annual profit can be deducted from the before tax profit and allocated to a fund, is the best of the alternatives which have been investigated. This fund is reduced if profits are negative. When distributed to the owners the company pays 80.8% tax on the money. Compared to the tax on dividends of 53.8% (no state tax is payed on dividends) this makes the allocation rule unprofitable for companies which do not expect to run into a deficit when the price is low. For the same reason the carry-back rule looks unprofitable in a deterministic model, when evaluating the expected present value of cash-flow to owners, and so there should be few arguments from the government point of view, using deterministic models, not to implement it. 43 refs., 60 figs., 44 tabs