The Powerball jackpot could be poised to explode.

The amount on the line tomorrow night is $260 million, or $134.2 million cash. The biggest in two years, it's Powerball's ninth biggest jackpot ever - and the 20th largest in U.S. lottery history.

If no one wins tomorrow, expect the prize to jump dramatically, perhaps to $300 or million or more. Only 10 U.S. jackpots ever got that large.

In August 2007, the jackpot soared to $300 million from $245 million - a lot less than tomorrow's drawing.

Powerball is getting a boost this time around in a couple of ways.

Its main competitor, Mega Millions, has a relatively puny top prize - a rock-bottom $12 million - for tonight's drawing.

That's because a North Carolina ticket had all the numbers Friday night, winning the annuity which was "just" $12 million, because a New York ticket hit for $64 million last Tuesday.

Also, Powerball's reach doubled in late January, when several dozen states began selling tickets for both major lotteries.

That means an even greater potential for sales to go wild as a jackpot grows.

The record U.S. jackpot is a $390 million Mega Millions jackpot, set in March 2007. A Cape May County couple and a Georgia man split that sucker.

Powerball's biggest was $365 million, hit by a single Nebraska ticket in February 2006.

The biggest prize won so far this year was a $266 million Mega Millions annuity hit early this month by a Calfornia couple.

Pennsylvania, New Jersey and Delaware are among the 40 states now selling both games.

Contact staff writer Peter Mucha at 215-854-4342 or pmucha@phillynews.com.