Six mutant lines of cotton (Gossypium hirsutum L.) with superior fiber quality were developed by the Department of Plant and Soil Science at Texas Tech University at Lubbock, TX, and released in 2019. Additional evaluations were conducted at Texas A&M University, College Station, TX, and at the USDA-ARS, Crop Genetics Research Unit, Stoneville, MS. Three of the lines, TTU 1-817 (Reg. no. GP-1076, PI 691517), TTU 1-1051 (Reg. no. GP-1077, PI 691518), and TTU 1-1283 (Reg. no. GP-1078, PI 691519), were selected from a mutant population of ‘Acala 1517-99’. Another three lines, TTU 2-411 (Reg. no. GP-1079, PI 691520), TTU 2-475 (Reg. no. GP-1080, PI 691521), and TTU 2-1073 (Reg. no. GP-1081, PI 691522), were selected from a mutant population derived from TAM 94L-25. Imbibed seeds of Acala 1517-99 and TAM 94L-25 were treated with 3.0% v/v of ethyl methane sulfonate (EMS). In 2002 (M2), 2003 (M3), and 2004 (M4), generations of the mutant populations were advanced by harvesting a single boll from each plant and bulking the seeds to generate the next generation. In 2005, seed cotton samples were hand harvested from a total of 3,122 individual M2:5 plants and evaluated for fiber quality. In 2012, 2013, 2014, and 2015, 33 of these M5 lines selected from the TAM 94-L25 mutant population and 30 M5 lines from the Acala 1517-99 mutant population were evaluated. Six M5 lines were selected and released for their longer, stronger fibers and lower micronaire.