Think about this: You are a righand. You live day to day, perhaps bottle to bottle. A). Do you have loads of cash to invest?
Ok, let's say you have money. You also have a cell phone and a broker. B). Do you buy the stock first, possibly having to sell later? C). Or do you save on trade fees and simply wait until you KNOW you have something (gas or oil) worth buying, in the first place?
C). makes the most sense, no?
That pretty much eliminates most insider selling, since obviously, most of 'those types' of insiders would not even buy, until they knew they had something worth buying.