At the top of the filter is a rubber seal. Sometimes when you remove the old filter that rubber seal stays in place and when you screw the new filter on the oil will spew out between the two seals....
Its possible you didn't properly install the oil filter. ie its miss-threaded or not tightened properly or too tight. You may have also left the old gasket from the old filter on. Also if you did not...
bad fuel pump
If the engine is running from a fuel pump that is NOT mechanically connected to the block, there is really only one way that fuel can get into the oil. It's usually from a...