This story assumes Ajdabiya has fallen to the loyalists who are preparing to move on Benghazi:
The Libyan army told residents of Benghazi to lay down their arms, ... and one of Gaddafi's sons, Saif al-Islam, told Euronews TV that Libya's second largest city would fall whether or not world powers imposed a no-fly zone.
Indeed, this story says the loyalists have Ajdabiya and, based on loyalist sources in Tripoli, will advance on Tobruk to the east. It also reports contrary sources that say the rebels still hold Ajdabiya.
Even Austin Bay, in discussing a potential advance on Tobruk and then Benghazi (and the failure of the international community to save the rebels), assumes Ajdabiya fell to the loyalists.
This story from yesterday says that rebels claim that while loyalists pushed into the city, the rebels still hold it:
By late afternoon, some of Qaddafi’s forces were seen in the city. But Khaled el-Sayeh, a spokesman for Abdel Fatah Younes, a former Qaddafi loyalist now in overall command of rebel forces, says the town remains in rebel hands.
At a press conference, Mr. Sayeh said that a few small units under the command of Qaddafi's son Saadi, a former professional soccer player, made it into the city. He said all of the men in those pro-Qaddafi units were killed, though he didn't know their numbers.
That action, mounted by rebel forces that remained in the city, caused Qaddafi’s forces to pull back, and there now a few kilometers west of the entrance to town, he said. “The city [Ajdabiya] is currently in the hands of the revolution and it’s looking pretty good,” he said. ...
Sayeh said that many rebel forces did withdraw from a line just west of the city under sustained aerial attack earlier today, and withdrew on the coastal highway without going through town. But he said those retreating forces were not joined by the bulk of the rebellion’s militia in the city proper. ...
This evening, an Ajdabiya resident said there were no more signs of fighting in the town, and that he too believed that whatever pro-Qaddafi troops had been present had withdrawn to the city's western outskirts.
This fits with my first speculation, although I admit that speculation stems from my initial reaction that the quick loyalist victory could not be true given the advantages of defending in a city provide the rebels.
Interesting, too, is that the rebels have gotten at least a couple aircraft in the air and claim to have sunk a couple Libyan vessels being used as warships.
I won't assume the Battle of Ajdabiya is over yet until I have clear indications that the rebels have lost. It makes no sense for the city to have fallen so quickly to the small loyalist force. But if it has, the rebels are in a world of hurt.
UPDATE: Oh, and the rebels captured a tanker at sea carrying refined gasoline on the way to Tripoli that would have fueled the loyalist war machine. What kind of stockpiles does Khaddafi have? Without fuel, his heavy armor advantage evaporates and the offensive could grind to a crawl just on that factor. Echoes of the World War II North African campaign. We don't need Ultra to pinpoint refined oil products. I wonder if anyone is tipping off the rebels to these shipments?