Millions will be glued to their TV sets when the Powerball numbers are drawn in a live event broadcast just before 11:00 pm eastern time (0300 GMT Sunday). If there is no winner, the jackpot could rise to close to $1 billion by the next drawing on Wednesday.
The jackpot is "the largest in the 21-year history of the game," the Iowa state lottery agency said in a statement.
Kim Chatman, a building security guard in Washington who plans to buy her lotto ticket after work, said "you've got to take your chance -- that's what it's all about."
The $2 tickets are sold at supermarkets, corner stores and gas stations in 42 states, the capital Washington and the US Virgin Islands.
In the midwestern state of Minnesota, tickets are even sold at fuel pumps and automatic teller machines.
"Strong sales across the country are the reason the prize is taking big jumps now," the Iowa state lottery agency said -- particularly after the May 15 drawing, when the jackpot stood at $363.9 million, and there was no winner.
Sales were also boosted after Powerball tickets became available in California starting in April.
The game is a choice of five numbers from a pool of 59, plus a Powerball number from a separate pool of 35.
Powerball -- a shared jackpot coordinated by the Multi-State Lottery Association (MUSL), a non-profit group formed by the participating state lotteries -- cannot be played from outside the United States or outside the participating states.
The richest US jackpot of all time was $656 million, won in a Mega Millions drawing in March 2012 and split between three tickets in Illinois, Kansas and Maryland. Like all US lotteries, the winnings are subject to tax.
Back then, "there were big lines for three days" of customers buying tickets, said Rajendra Prasad Bhusal, who works at the Continental Wine and Liquor store in downtown Washington.
That's when the tickets cost $1. "Now, people complain that the tickets cost too much," he said.
In recent days, customers have streamed in to buy Powerball tickets, but the crowd is only a third of the numbers seen in March 2012, according to the liquor salesman.
The Powerball website says the odds of winning the jackpot are one in 175,223,510. For a comparison, the odds of getting struck by lighting in the United States is one in 280,000, according to the National Lightning Safety Institute.
The main Powerball website advised that "swinging a live chicken above your head while wishing for the future numbers does NOT work" to improve the chances of winning. "There is no improvement to be had by swinging a dead chicken," it added.
Buying more tickets helps, "but the odds are still high and hitting the jackpot is still a question of fate," it said.