Major oil companies have reported 2008 profits that would make automakers weep. Perhaps even a few motorists.

In a year that saw the national gasoline price average rise to $4 a gallon, then within a few short months plummet to $2, Exxon Mobil set a record for the most profitable American corporation on $45.2 billion in earnings. And this despite a fourth quarter that saw a 33-percent drop in profits, due in part to dropping oil prices.

Exxon Mobil wasn’t alone in raking in big numbers. Chevron, for instance, reported $24 billion in profits. By themselves, these figures are staggering, though Bloomberg.com put it in an interesting context when it wrote: “Exxon Mobil’s and Chevron’s combined revenue for 2008 exceeded the gross domestic products of all but 16 of the world’s nations.”

Another perspective would be to look at what these firms could buy. For instance, today’s market cap, or present value, for General Motors is about $1.8 billion and Ford Motor Company is $4.4 billion. Despite the significant decline in earnings, Exxon Mobil cleared $7.8 billion in the last quarter—more than enough to purchase both industrial giants and still have money left over to aid in restructuring. Repeat: In just one quarter.

Carrying this theme, Wall Street rewarded itself with a reported $18.4 billion in bonuses for 2008. Quite literally, a Manhattan office pool could buy a troubled automaker these days. In fact, you might even get a division for free. But I digress.

All this has me thinking: What if an oil company bought an automaker? What would it do, and what kinds of vehicles would it produce? What if Wall Street did? I have my thoughts, but would be interested in reading yours in the comments below, or in the forums.