Wrestling for control in Libya's tricky war
The battle for eastern Libya is approaching some crucial hours, as government and rebel forces compete to control the motorway that leads to the rebel stronghold of Benghazi.
For a time at the weekend, it seemed as if the government advance was unstoppable.
But at dusk on Sunday evening, rebel forces moved back into the oil town of Brega. It is an illustration of the problems that still face Col Muammar Gaddafi's forces as he attempts to regain control of Libya.
The rebel commander, Gen Abdul Fattah Younis, reminded a news conference on Sunday of the special nature of desert warfare.
With so few settlements, large swathes of territory can be captured very quickly, and lost just as fast.
That is even more true in the Libyan case, where relatively small forces are battling over a very large area.
Col Gaddafi's big advantage is the superior firepower, air power and sea power he has at his disposal. In the case of the oil towns of both Ras Lanuf and of Brega, it has meant he can bombard them into submission.
But as he has found in Brega, it is harder to hold onto his gains. He has limited numbers on the ground, perhaps only a maximum of a few thousand troops in eastern Libya, and his supply lines are becoming ever longer.
And his problems can only get bigger if he does manage to push further east.
The next town on the road, Ajdabiya, is much bigger than Brega.
The population numbers anything from 50,000 to 100,000, almost all of them fierce opponents of Col Gaddafi.
The troops could take to the desert and skirt round the outside of the town, but that would leave their communication lines even more exposed.
As for the rebel stronghold of Benghazi, that is of a different order altogether. It is a city of one million people, most vehemently opposed to Col Gaddafi, many of them armed.
A frontal assault is unthinkable at the moment, with the scale of government forces and their long supply lines.
Another option for Col Gaddafi is to try and consolidate either in Brega or possibly in Ajdabiya. That would give him control of a key crossroads, with the scope potentially to cut off large parts of eastern Libya.
But again, he risks leaving the rear of his forces exposed, and giving time for the opposition to build up their rudimentary military machine and possibly begin a campaign of guerrilla warfare.
Ideally, Col Gaddafi would like to stifle resistance in the west, then move reinforcements further east.
But that is taking longer than he might like, with reports of disagreements and even battles amongst his forces, as some government troops baulk at being asked to attack civilians in the city of Misrata.
Of course, the opposition face equally serious problems.
It is hard to see how they can regroup and push back any distance to the west.
They need heavier weapons, better trained troops, and some answer to Col Gaddafi's air power.
The eastern cities are also vulnerable to possible disruption of their power, water and communications.
Though so far, the threat of a no-fly zone seems to have deterred Col Gaddafi from bombing Benghazi or other major population centres in the east.
On the face of it, the military balance suggests a deadlock.
But the terrain, the small number of forces and other factors such as possible foreign intervention mean it is a very fluid situation.
Advantage can swing very rapidly from one side to the other.
It is difficult to make any snap judgements about who is winning and who is losing.