This study will compare capecitabine/oxaliplatin as adjuvant chemotherapy versus observation alone in chemotherapy-naive participants who have undergone potentially curative resection for gastric cancer. Participants will be randomized to either the chemotherapy arm or the observation arm. Capecitabine will be administered orally, 1000 milligrams per meter-squared (mg/m^2) twice daily (BID) on Days 1 to 15 of a 3-week cycle, for 8 cycles, and oxaliplatin will be administered as an intravenous (IV) infusion, 130 mg/m^2 every 3 weeks for 8 cycles. The anticipated time on study treatment in 6 months and the target sample size is 1024 individuals.

Inclusion Criteria:

• Adult participants greater than or equal to (>=) 18 years of age
• Gastric adenocarcinoma, Stage II, IIIa or IIIb
• Potentially curative resection of tumor within 6 weeks prior to randomization
• Previously untreated with chemotherapy or radiotherapy

Exclusion Criteria:

• Serious concomitant medical illnesses that would limit life expectancy to less than (<) 5 years
• Sexually active males and females (of childbearing potential) unwilling to practice contraception during the study
• Any evidence of metastatic disease (including presence of tumor cells in the ascites)