Oil prices are tanking again today to lows not seen since the depths of the '08-'09 recession.

A barrel of West Texas Intermediate (WTI), or light, sweet crude oil, fell 1.5 percent to $45.33.

The national average for a gallon of gas has fallen to $2.12, and it's looking increasingly likely that the entire country will see gas below $2 before the end of this month.

Read More: Gas Prices Fall Again, With No Floor in Sight

Oil is one of the big drags on stocks today. After starting the day positive, the S&P 500 and Dow Jones Industrial Average have now turned negative.

What's causing oil to fall? A number of factors, including increased U.S. production, continued flow by OPEC nations in spite of a worldwide glut, and an economic slowdown in Europe leading to lower demand for petroleum.

Now 45 states have at least one gas station with gasoline under $2 a gallon, according to GasBuddy.

The only states without $2 gas are:

- Alaska

- Hawaii

- Vermont (cheapest station at $2.17)

- California (cheapest station at $2.13)

- Pennsylvania (cheapest station at $2.02)

ABC News' Zunaira Zaki contributed to this report.