The study investigated the application of generalizability theory in estimating dependability of public examination essay questions in English language. The design is ex-post facto and two facet fully crossed G-Study and D- Study. The population was 36,705 senior secondary students. Taro Yamane formula was applied to estimate the sample from the population using multistage sampling procedure, simple random sampling techniques and purposive sampling technique to select 420 senior secondary school students who registered for both West African examination council and National examination council in Rivers Stat. The instruments were West African Examination Council and National Examination Council essay questions papers 2018.The data obtained were analysed using Variance Component; G-Study and D-Study calculated by applying Felaye’s formula. Results showed items variance components contributed high, generalizability coefficient and index of dependability are low 2018 essay questions in English language West African examination council and Students variance components contributed high, generalizability coefficient and index of dependability relatively high in 2018 essay questions in English language conducted by National examination council. Recommendations, public examination bodies should store verified psychometric properties essay questions in English language in their item bank for sales to users, they should create community of data analyst especially with estimation of Generalizability theory. Students should be encouraged by both parents and teachers to study hard, since exit examination are for certification which is a criteria for tertiary institution admission. Test developers should be consistent with syllabus in arranging test items. Raters should be trained on rating skills to maintain rater agreement School administrators and education managers should provide conducive environment and support for conduct of examinations by public examination bodies.