The sheer volume of the oil dump now becomes a key factor in the third phase of the trial, due to begin January 20. Under the Clean Water Act, Barbier is obliged to assess the extent of the spill in light of a series of factors that include the polluter's attempts to contain the disaster once it got under way, the economic effects of the penalty on the company, the benefits BP enjoyed from operating the way it did before the spill, and the company's history of other violations. BP could end up on the hook for an amount ranging from single-digit billions of dollars up to the $13.7 billion ceiling.