Phase two of the trial pitting BP against the federal government opens on Monday, as the court tries to decide how much to fine the company for the 2010 oil spill in the Gulf of Mexico.  The biggest question in this phase will be:  How big was the spill?

In the worst case, BP could be fined more than $17 billion — a bit more than the company’s profits for 2012. 

The fine will be based on a simple equation:  A dollar amount per barrel of oil (probably in the thousands)  times the number of barrels of oil spilled.  In the next weeks the court will hear about the how-many-barrels part.

The feds and BP have both submitted estimates, and they’ll both put experts on the stand to say why their number is better. 

According to law professor David Uhlmann from the University of Michigan, here’s where the court’s problems begin.  There’s no way to really know.

“There weren’t any meters,” he says. “There wasn’t any measuring device.  There’s no way to determine precisely how much oil was spilled.” 

Here’s where the company’s track record so far could hurt it. Loyola University law professor Blaine LeCesne says BP has repeatedly put out numbers that lowballed its liability.

“I think when you cry wolf enough, at some point it could affect your creditability on other issues down the line.”

If that’s how the judge sees things, it could make a several-billion-dollar difference to BP.