The game is for two players, using three suits from a standard 52-card pack. Cards rank Ace (low), 2, 3, 4, 5, 6, 7, 8, 9, 10, J, Q, K (high). As a prize, the Ace is worth 1 point, cards 2-10 face value, Jack 11, Queen 12 and King 13.
The cards are sorted into suits (diamonds, hearts, spades, and clubs). Diamonds is shuffled and stacked face down as a prize pile. Each of the other players takes one of the black suits (spades and clubs). You can look at all 13 of your cards in your hand.
You win GOPS by using your cards to bid on the prize pile cards that come up each turn.
The top card of the prize pile is turned face up. Then each player selects any card from their hand with which to bid for it and places it face down. When both players are ready, the bid cards are revealed simultaneously, and the higher bid wins the prize card. The bid cards are then discarded and the prize card is placed beside the player who won it. The next card of the prize pile is turned face up and players bid for it in the same way.
If the bids of the two players are equal, the bid cards are discarded but the prize card remains on offer. A new prize card is turned face up and the next bid is for the two prize cards together, then for three prize cards if there is another tie, and so on. If the player's last bid cards are equal, the last prize card (and any others remaining from immediately preceding tied bids) are not won by either player.
When both players run out of bid cards the play ends. Each player totals the value of the diamonds they have won in bids (ace=1, 2-10 face value, J=11, Q=12, K=13) and the greater total wins the game.