Introduction: This research explored the Effects of Casualization on the Welfare of Workers using a de-identified multinational oil company in Nigeria as a representative case. Objectives: The objectives of the study were to examine the effects of casualization of workers, associated irregularity of work, and deprivation of workers’ right. Methodology: A close-ended questionnaire was used to collect primary data. Out of 150 copies of the questionnaire administered, 122 were dully filled, returned and analysed using descriptive statistics. Results & Discussion: Three hypotheses were proposed and analysed using multiple regression of ordinary least square (OLS) statistical method and tested at 0.05 level of significance for the hypotheses. The result showed that there were significant negative effects of casualization of workers for a short-term contract work, irregularity of casualization of work, and deprivation of workers right to negotiate. Conclusion: Hallmarks of casualization of labour include short term contract work; irregularity of work; and deprivation of workers’ right to negotiate adversely affects the welfare packages of workers. These practices have inherent occupational health implication on workers. Recommendations: Casualization of labour as seen in this study is a despicable model that should be discontinued. However, if it must be practiced, the human resources, industrial relations, labour union and occupational health experts in such organizations should repackage such contracts to include allowances, job security, negotiation rights, dignity, benefits and welfare clauses as in permanent full time employment.