It opens in 1918 as John "Big John" McMasters (Gable) and John "Square John" Sand (Tracy), two roughneck oil wildcatters, descend on the Real Life oil boom town of Buckburnett, Texas. They team up, and after stealing some drilling equipment, strike oil. Around this time, a woman Square John has been courting, Elizabeth Bartlett (Colbert), comes to Buckburnett to see him. Unfortunately for Square John she meets Big John coming off the train instead, and because he's Clark Gable, she falls in love with him. Sand is hurt but masks his feelings. The sting of McMasters and Elizabeth getting married is lessened somewhat when they both get rich off the oil wells they've dug.
A year passes and the two Johns are wealthy oil men. Sand still carries a torch for Elizabeth, however, and when he catches McMasters fooling around with the local dance hall girls, he's outraged. They flip for their oil field, Sand wins, and Big John goes off broke, Elizabeth in tow, looking for the next likely wildcat location.
Cycles of boom and bust come and go for each of them. Big John and Elizabeth have a son. Finally McMasters is a fabulously successful oil tycoon, and Sand is working with him. But when Big John starts cheating on Elizabeth again, this time with an exotic European beauty named Karen (Lamarr), Sand feels he has to take drastic action.
- Banana Republic: Somewhere in "the tropics" is where Sand makes one of his fortunes. He's shown someplace where palm trees grow, paying off a general. He loses everything when "the other side" wins a war.
- Boom Town: There's a Boom Town in Boom Town! Namely, Buckburnett, Texas, a Real Life boom town shown at the moment where the population was going up by a factor of ten as oil men started swarming down on the town.
- Conversation Cut: Big John's sales pitch to stop the other oilmen from supporting Sand and Compton is spread over several scenes, with Clark Gable's dialogue transitioning seamlessly from scene to scene as he gets the wildcatters to back him.
- Drowning My Sorrows: There's a quick shot of Sand drinking in a bar after finding out about McMasters and Elizabeth, but it's only the first part of a Time Passes Montage that shows them building their first oil empire.
- Edgy Backwards Chair-Sitting: Sand does this when asking Karen to marry him. He doesn't even like her very much, but he wants to stop her from breaking up Big John and Elizabeth, so he asks Karen to be his Trophy Wife.
- Fourth Date Marriage: After one evening strolling around town together, McMasters and Elizabeth get married.
- It Will Never Catch On: As the gang walks around their new wildcat oil field, Luther scoffs, saying "There's a dry hole in every foot of this stuff!" Their land is in the Kettleman Hills, and the last shot shows the ocean of oil derricks there.
- Match Cut: From Big John scrubbing laundry in a washtub to the coupling rods of a train engine chugging, as he and Elizabeth go to the next job.
- Meet Cute: A non-romantic version thereof, as the Johns meet in the middle of a single plank that has been laid across a muddy street as a crossing. Each tries to intimidate the other off—until a shootout breaks out and they both dive into the mud for cover.
- New Old West: The film opens up in Buckburnett, Texas, which is the picture of a Wild West town, with crudely constructed wooden buildings, wooden boardwalks, dance hall girls, cowboys, horses, and streets that are nothing but mud. Except the date is 1918 and people are driving cars as well, and the treasure being hunted is oil and not gold.
- Romantic False Lead: Sand, who has no chance with Elizabeth.
- Title Drop: "These boom towns reek of larceny," says Luther when Sand tries to get him to loan the equipment for the well.
- While You Were in Diapers: As Sand and McMasters argue about where to sink their first well, the latter says "I was pulling oil out of the ground when your ma was giving it to you for your health."
- You No Take Candle: A super-racist scene has a Native American on Big John's oil field say "Him like me very much."