I have to 10 gallon aquauriums I have never used so I decided to fill each with 37.95 liters of tap water and added 35 grams of non iodized salt to each. I let both tanks vent cholorine for 6 hours and equalized the temperature for both at 77 degrees in my laundry room. Each tank had a 100 watt spot light two feet above the tank with thermometers in each tank. Beneath each tank was tan construction paper wchich showed through the bottom of the tank.

I added one teaspoon of 30 weight motor oil(4.92892159 milliliters) to one tank only and turned on both lights and took temperature readings of the water every hour. The thermometers were on the bottom of the tank and edgwise to the light.
The oiled tank had a sheen but did not take on a black appearence like some parts of the gulf shore.

After an hour the tank with oil was 1.5 degrees higher while the the clean tank had only raised half of one degree. I assume that the inhibition of cooling evaportaion was the main factor since the color of the oiled water was not a solid dark color.

After 2 hours the room had gone up to 78 and the oiled tank was 80 degrees and the clean tank was just under 79 degrees.

The next day I put 9 more teaspoons of motor oil in the oiled tank and compared heating. Room temp was 76. After 2 hours room temp was 77 and the oiled tank was just under 82 degrees compared to the clean tank at 78 degrees.

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While I can not reasonably extrapolate these rates of heating to the Gulf of Mexico oil spill, it is safe to say that oiled water heats significantly from a hot light source more than clean water.

If I used dirty black oil I am certain that the oiled tank temperatures would be even higher.

Under hurricane conditions I wonder how much the effect of limiting cooling evaporation and adding significantly more heat to the water will have of the strength of a storm.

As water retains heat better than air or land, oil retains heat better than water. While I have no proof or certainty, this may not bode well for this hurricane season.