Petroleum firms in Kenya operate within a competitive, volatile environment shaped by price fluctuations, infrastructural gaps, and regulatory changes. This study investigated the effect of competitive strategy on service delivery among petroleum firms in Nairobi County. Using a descriptive cross-sectional survey design, the study integrated both qualitative and quantitative methods. From a target population of 324 service stations, 125 managers were selected through stratified random sampling. Data were collected using semi-structured questionnaires and analyzed with SPSS version 28, employing descriptive statistics and regression analysis. Results revealed a positive and statistically significant relationship between competitive strategy and service delivery (β = 0.717, p = 0.000). Key strategic drivers included service innovation, technology adoption, and employee satisfaction. The study concluded that firms prioritizing competitive strategies experience improved service quality and responsiveness. It recommends continuous investment in technological advancement, customer-focused initiatives, and strategic partnerships to enhance service performance in the petroleum sector.