DES MOINES, Iowa (AP) -- The Mega Millions jackpot has soared to an estimated $1 billion, as the second-largest lottery prize in U.S. lottery history gets even bigger.

Lottery officials increased the grand prize just hours ahead of the Friday night drawing. The prize climbed from $970 million.

Although the jackpot keeps increasing , the odds of winning remain stuck at a miserable one in 302.5 million.

The prize has grown so large because no one has hit the jackpot since July 24, when a group in California won $543 million.

The $1 billion prize refers to the annuity option. Most winners opt for cash, which for Friday night's drawing would be $565 million.

Officials say that if there isn't a winner, the prize for Tuesday night's drawing would be $1.6 billion, tying the largest U.S. lottery prize.