Several news outlets are reporting this afternoon that the Libyan rebels have taken a major step forward in their advance on Tripoli by capturing an oil refinery in the northwestern coastal city of Zawiyah, which serves as a major source of fuel for Muammar Qaddafi's troops and sits only 30 miles away from the capital (the picture above shows rebel fighters destroying Qaddafi posters found in the refinery). While the oil refinery itself may be in opposition hands, fighting between the rebels and Qaddafi's forces is still raging elsewhere in the city. The BBC explains that control of Zawiyah would allow the rebels to surround Tripoli by land and NATO to encircle the capital by sea. In a further sign that the Libyan regime's supply lines may be imperiled, Reuters is reporting that the rebels have also captured the ancient Roman town of Sabratha on the coastal road between the Tunisian border and the capital. 

We've noted before that the rebels face long odds in taking Tripoli and that they've approached the capital before, only to be repulsed by government troops. But there are signs this time may be different. While the rebels have suffered from internal divisions and poor training, The New York Times notes, Tripoli looks increasingly vulnerable, with people fleeing the capital reporting no electricity and soaring prices for basic goods. British defense expert Malcolm Chalmers tells CNN that NATO's "war of attrition" and recent rebel gains on the ground appear to finally be taking their toll on Qaddafi's forces, adding that he doesn't expect the Libyan military to last "more than one or two months, maybe less." But Simon Henderson of the Washington Institute for Near East Policy adds that "it's still too early to say that the end of this is going to be a complete defeat of Qaddafi's forces." For more color on the battle for Zawiyah, check out this audio recording from Sky News correspondent Alex Crawford, who's on the ground in the contested town: