DES MOINES, Iowa » The Mega Millions jackpot soared to an estimated $636 million on today, making it the second largest lottery jackpot in U.S. history.

The top prize had been estimated at $586 million, but lottery officials increased their prediction this morning because of strong ticket sales. The jackpot now trails only a $656 million Mega Millions pot that was sold in March 2012.

Mega Millions changed its rules in October to help increase the jackpots by lowering the odds of winning the top prize. That means the chances of winning the jackpot are now about 1 in 259 million.

But that hasn’t stopped aspiring multimillionaires from playing the game.

"Oh I think there’s absolutely no way I am going to win this lottery," said Tanya Joosten, 39, an educator at the University of Wisconsin-Milwaukee who bought several tickets today. "But it’s hard for such a small amount of money to not take the chance."

Annie Pedersen also said she wanted to be part of the action, so she jumped in and bought two tickets at a Milwaukee grocery.

"Everybody is so excited about it so I wanted to get in on some of the excitement, too, by watching," she said.

Tickets are selling at a pace that surpassed even the lottery’s expectations.

"We estimate by drawing time we’ll be about $75 million ahead in sales," said Paula Otto, executive director of the Virginia Lottery and lead director for Mega Millions.

Otto said officials expect about 70 percent of the possible number combinations to be purchased for tonight’s drawing. She also noted that if a winner isn’t selected either tonight or for Friday’s drawing, the jackpot could hit $1 billion — an unheard of amount for Mega Millions or Powerball, the nation’s two main lottery games.

The drawing is scheduled for 11 p.m. EST. The cash option is estimated at $341 million, before taxes.

The previous odds of winning Mega Millions’ top prize were roughly 1 in 176 million, nearly the same as Powerball, which also has seen a surge in large jackpots since its rules were revamped in January 2012.

Mega Millions is played in 43 states, the District of Columbia and the U.S. Virgin Islands.

Associated Press writer Carrie Antlfinger contributed to this report from Milwaukee.