An increased density of Helicobacter pylori in the gastric mucosa can be associated with more severe gastritis and an increased incidence of peptic ulcers. Therefore, people with asymptomatic gastritis would certainly benefit from a nutritional approach to help them manage the infection and therefore decrease the risk of development of associated pathologies. We analyzed the activities of 60 essential oils against H. pylori P1 and identified 30 oils that affected growth, with in vitro inhibition zones ranging between 0.7 and 6.3 cm in diameter. We further analyzed the effects of 16 oils with different activities on H. pylori P1 viability. Fifteen showed strong bactericidal activities, with minimal bactericidal concentrations after 24 h ranging from 0.02 to 0.1 g/liter at pH 7.4. Even though slight variations in activities were observed, the essential oils that displayed the strongest bactericidal potentials against H. pylori P1 were also active against other Helicobacter strains tested. Among the pure constituents of different essential oils tested, carvacrol, isoeugenol, nerol, citral, and sabinene exhibited the strongest anti-H. pylori activities. Although oral treatment of H. pylori SS1-infected mice with carrot seed oil did not result in significant decreases in the bacterial loads in the treated animals compared to those in the control animals, in all experiments performed, the infection was cleared in 20 to 30% of carrot seed oil-treated animals. Our results indicate that essential oils are unlikely to be efficient anti-Helicobacter agents in vivo. However, their effects may not be irrelevant if one plans to use them as food additives to complement present therapies.