Twelve upland cotton (Gossypium hirsutum L.) cultivars, released by the oklahoma Agricultural Experiment Station between 1918 and 1982 inclusive, were evaluated for years under dryland and irrigated conditions at two locations. Other experiments were planted at a third location to measure resistance to two diseases and at a fourth location to evaluate reactions to yet another disease. The objective was to determine selection progress over time in the cotton breeding program for yield, fiber properties, agronomic characteristics, and resistance to disease. Where appropriate, regression analyses were performed to quantify those breeding trends. Analyses of variance detected significant differences among cultivars for yield, all fiber properties, all agronomic characteristics, and two diseases. Lint yield increased 2.3 kg/(ha yr) under dryland and 3.3 kg under irrigation. A yield plateau for cotton has not yet been reached in the state. Increases of 0.04 to 0.05 mm/yr for 2.5% and 0.02 mm/yr for 50% span fiber lengths were observed. Uniformity index and micronaire displayed no significant trends over time. To fiber strength increased by 0.5 kN m/(kg yr). A quadratic equation best fit T(1) fiber strength; however, since the mid-1940s, its trend has been generally upward in a linear fashion. Picked and pulled lint percent increases are initially rapid, but have reached a plateau in recent decades. Bolls required to produce a given quantity of seedcotton have generally been decreasing in number. Boll size has increased, but bur size played no significant trend over time. Might of lint/boll increased over the first three cultivars released, but has since remained essentially constant. Relatively large improvements were made in lint index between 1918 and 1964 inclusive. Since then, cultivars have exhibited similar lint indexes. Seed weight increased by 0.0 g/yr under dryland and by 0.03 g under irrigation. Lock tenacity increased by 1.7 g force/yr. Trends over time were noted for resistance to bacterial blight [causal organism: Xanthomonas campestris pv malvacearum (Smith) Dye] and to fusariun wilt [Fusarium oxysporum Schlect. f. sp. vasinfectum (Atk.) Snyd. & Hans.]-root-knot nematode [Meloidogyne incognita (Kofoid & White) Chitwood] complex, but not to verticillium wilt (Verticillium dahliae Kleb.).