The same company responsible for shutting down the pipeline, British Petroleum, was recently charged with market tampering with propane prices so they certainly have proven they have a propensity for this kind of thing.
http://www.consumeraffairs.com/news0...p_propane.html
Please notice that one of the witnesses against BP, a former trader plead guilty to what? Conspiracy.
As for your arguments about demand, they're nothing short of baseless. There is no shortage of oil, and OPEC has offered to increase production if necessary multiple times. The US does not refine gasoline for other world markets before supplying it to the US markets. Furthermore, oil companies have readily admitted to controlling gasoline prices in the interest of curbing demand to prevent shortages. This flies in the face of the reality that increased gasoline prices has not resulted in a signficant reduction in gasoline purchases.
The mere fact that oil companies admit to controlling the price of gasoline is enough to warrant investigation. Multiple companies working together to keep prices artificially high is called price fixing.
http://www.breitbart.com/news/2005/11/09/D8DPB2900.html
http://www.msnbc.msn.com/id/13404319/
There is always a burden of proof to be met in order to take accusations seriously, and in the face of the non-stop excuses spoon fed to the American public amidst world record setting profits, there is simply no room for doubt here.