If it was about oil we'd still be cosying up to Gaddafi in exchange for lucrative contracts (see BP, etc). He went and spoiled it all by massacring his own people.
It's a collective short-term memory loss going on here. In the 80s we bomb him (OK, the US do) for sponsoring terror. Then there's sanctions for years which half-bankrupt his economy. Then when he starts making conciliatory noises over Lockerbie, Chemical weapons and so on, we welcome him into the fold and start selling him copious amounts of 'clean' weaponry. Talks are held, deals are done, contracts are signed. Then his people catch a contagious whiff of 'democracy' from the neighbours, he falls back into 'mad dog dictator' mode and starts slaughtering them. If we sit back and let it happen we're guilty of putting business interests over human rights. Imagine the outcry - oil for blood. West ignores Libyan genocide (I've heard the G Word said half a dozen times now, for some reason) to safeguard oil interests. "Just like Iraq", they'll all cry, without knowing anything about Iraq, or much about Libya either.
Three things going on here: potential humanitarian crisis on Europe's doorstep. Italy/Spain/Greece/Malta don't much want to be swamped with Libyan refugees fleeing Gaddafi's genocide. Something must be done. Stung by accusations of inaction over Rwanda, if there's a chance of genocide they'll be on it fast. Too bloody fast. They were awfully quick to start justifying this military action in case it did happen.
Second, vested interests: big business contracts to be had in Libya which has been in isolation for a long time (not just oil). If Gaddafi is dragging his feet, playing hard to get, "Let's give the old bastard a push if he's outlived his usefulness". Strategic and economic interests are a huge factor in all this. But let's not oversimplify things with the oil conspiracy.
Third, our leaders have started to believe their own propaganda. They all got a bit carried away with the giddy rush of North African democratization and thought Libya would follow suit of its own accord. Problem is, they jumped the gun a bit. So what do we do? What worked for Saddam? I know - no-fly zone, a.k.a regime change. US/UK/NATO are the new global policemen. It has somehow become accepted that each week, dozens of civilians are going to be killed in drone strikes, whether in Afghanistan or Pakistan. The howls of protest are deafening only by their absence. But we've got form - it happened in Laos, and again in Cambodia, and we're still rewriting the history over that one.
So once again we see US/UK/NATO missiles heading off for $islamiccountry. I saw it live on TV in the 80s, I've seen it a dozen times since and I'm seeing it again now. The BBC commentator today said "Colonel Gaddafi must be regretting his defiance of the international community now, as Strike Phantom Task Force WTF disperse his troops with their smart weaponry". Bastard nearly jizzed his pants with excitement as he said it.