Having argued a few days ago that a partition between East and West in Libya might be an outcome based on their long history of disunity and numerous differences, I am now thinking that this is a very unlikely outcome for a variety of reasons, although oil and geography are at the top of the list.
So, for a stable partition, it would probably need to be the case that there would be a relatively even split of the oil revenues between the two sides. However, of the six oil terminals in Libya, four are clustered near each other at the east end of the Gulf of Sidra and have changed hands between the two sides. Currently Qaddafi's forces control three of them, but the most intense front line of the battle appears to be happening at Ajdaibiya (sp?), where according to Juan Cole, the rebels are gaining strength and control. For anything other than a 5-1 or 1-5 division of the terminals, a stable line would have to be established drawn through the middle of these terminals, but this looks extremely unlikely to me. One side or the other will probably take them and whoever does so will win overall.
Another fact is that while in general the rebels are stronger in the East and Qaddafi's supporters in the West, the rebels continue to have support in and control certain locales in the West, with the new Allied air strikes helping them defend those locales, particularly Misurata, the third largest city in Libya, and Zaitan in the southwest. Qaddafi's strongest base, his hometown of Sirte, is east of those cities. There simply is not a neat division and I suspect that there will not be.
Moving beyond this basic oil-geography issue, there are other matters. One is that both sides appear determined to claim total victory. The only way that such a partition will occur is if there is a stalemate after long fighting, but I think other dynamics are at work, with Juan Cole pointing to the volatility of tribal loyalties. In this case, the key tribe is Libya's biggest, the Warfalla, at 1 million nearly a sixth of the whole population, who happen to have a major base in rebel-held Misurata. The Warfalla have long been among Qaddafi's strongest supporters, fellow Arabized Berbers (although with more intermarriage with real Arabs than in Qaddafi's tribe), and long providing many of his innermost staff and guards, despite leading an attempted coup in 1993.
As it is, the Warfalla are reportedly vacillating, possibly having shifted back and forth twice already in this conflict. But they may not wish to have a stalemate, and if they tilt strongly to the rebels, this might tilt things in the rebels' direction, leading to a major move in the military to stop supporting Qaddafi, particularly given the apparent unwillingness of the military to fight too much against the Allied air strikes (and with the Libyan air capapbility reportedly shut down pretty much already). The word of actual Arab support for the Allied force from Qatar and UAE (the only two Arab nations not to have had any demonstrations or uprisings so far in this Arab Spring) may add to this impetus, along with the withdrawal of the US from commanding it to behind the skirt of NATO, with formerly opposed Germany and Turkey now acquiescing.
Adding further to this is that the US and French and others appear to be becoming more enthusiastic about the rebel leadership. There has been much muttering about Islamist influences (and the former king Idris was the grandson of one of the founders of the radical Islamist Salafi movement), but the new leader of the provisional government, which has now established a central bank and oil company, Jibril Mohammed, got a PhD in strategic planning from the U. of Pittsburgh and appears to be a pro-western secularist, even described as a supporter of "neoliberalism" in his newly written (with misspellings) Wikipedia entry. Expect this to encourage stronger external support for the rebellion, which will seek to topple Qaddafi, even if Germany and Turkey mumble unhappily (and Putin and Medvedev argue over whom Russia should support).
However, the key to the outcome will be if the Warfalla and other tribes that have been supporting Qaddafi, as well as their members in the military, decide that it is not worth it supporting him any longer. If they turn on him, it will be all over. But the bottom line looks like it is much more unlikely than I previously thought that there will be any sort of stable partition as an outcome of all this.