Just in time for Memorial Day weekend, the official start to the U.S. driving season, refineries are finishing maintenance and other planned outages to boost production of refined products.

For thirteen consecutive weeks, total motor gasoline inventories have fallen. One would have to go back to February to find the last weekly Energy Information Administration report that showed an increase in total gasoline inventories. Much of the reason for declining inventories was due to a switch-over in the type of gasoline consumed (as required by the EPA), but also because of refining issues. Most notably, a fire at BP's Cherry Point, Washington refinery back in mid-February.

Many facilities have completed maintenance, but there are several still working on completing maintenance and ramping up production to meet increased seasonal demand. Refineries soon coming out of maintenance include Citgo's refinery in Lemont, IL, Sunoco's Philadelphia refinery (soon to be owned by Energy Transfer Partners), BP's Cherry Point facility, and Valero's refinery in Meraux, LA.

What we've seen this year is a jump in refinery utilization compared to last year, which is helping prices stay lower than they were one year ago. However, in checking with how much of available capacity refiners were using, we've seen a drop since a decade ago. In 2003 for example, refiners used an average of 95.3% of their capacity. Of course, back in 2003, we had more refineries online, so there was more product being supplied. Utilization has dropped steadily since then. Here's a look at the average utilization for the month of May for U.S. refineries.

May 2003: refiners utilized 95.3% of capacity
May 2004: refiners utilized 95.2% of capacity
May 2005: refiners utilized 94.2% of capacity
May 2006: refiners utilized 90.3% of capacity
May 2007: refiners utilized 90.2% of capacity
May 2008: refiners utilized 87.4% of capacity
May 2009: refiners utilized 84.4%* of capacity (recession)
May 2010: refiners utilized 87.9% of capacity
May 2011: refiners utilized 84.3% of capacity
May 2012: refiners utilized 87.4%* of capacity (thru mid-May)

As you see, utilization seems to have been dropping for the last few years. This highlights the importance that refiners play and how low production increases prices of gasoline. Hopefully in the next few weeks as refiners finish maintenance we'll see utilization take a small jump- it certainly would be helpful to see gasoline inventories rise. For now, all eyes will be on tomorrow's EIA weekly report to find that out.