My numbers were for illustration. It doesn't need to be 10x more profitable, it just needs to be any degree more profitable and the unlucky event sufficiently rare that the profit of the successful wells outweighs the costs of the failure (also keep in mind that oil companies drill many, many unsuccessful wells, so a marginal increase in the cost of drilling an exploratory well is significantly magnified).

Despite the costs of cleanup, we're not anywhere near the point where it makes sense for them to change their practices. BP made $4bn in profit last year, and current cleanup costs have yet to hit $1bn. They can get a lot, lot higher before they outweigh the profits of years of risky drilling.