An independent trust fund discourages investment.  When it is politicians who control both the investment and the amount funds being returned from that investment then they have an incentive to encourage more investment. They will want more exploration to find more resources, they will promote technological advances to be able to extract more from the same fields, and they will be willing to grant more production licences.  If on the other hand the money goes into a trust fund then the government and parliament has little incentive to encourage the market and every incentive to hold it up. The oil only provides a risk; unpopularity due to environmental impacts without any benefit in return.  The result will be that the costs of drilling will be seen in the environmental damage it causes while communities do not get any of the benefit as the money is being squirreled away ‘for the future’. This is hindering the market and so reducing the economic benefits to the country.