The concentration of CO2 in the upper layer of the world's oceans is higher than is found in air, and thus it is the most concentrated "mine" from which zero-net carbon fuels can be produced. The U.S. Navy estimates that a typical nuclear propelled aircraft carrier which generates 100 megawatts of electricity can produce 41,000 US gallons(155,202 litres) of jet fuel per day and production from the onboard nuclear reactor would cost about $6 per gallon($1.58 per liter). While that was about twice the petroleum fuel cost in 2010, it is expected to be much less than the market price in less than five years if recent trends continue. Moreover, since the delivery of fuel to a carrier battle group costs about $8 per gallon, shipboard production is already much less expensive. Heather Willauer of the United States Naval Research Laboratory proof-tested the technology in 2013, fueling an internal combustion engine equipped model airplane with the synthetic fuel.