Light, sweet crude oils are depleting, forcing oil and gas companies to explore and operate in increasingly deeper waters, remote geographical locations and harsher environmental conditions with higher safety risks. This paper analyzed the common misuse and errors of typical quantitative risk assessments (QRAs) during identification, assessment, approval and project implementation stages of a project for the case of optimization of facilities and manning fixed offshore oil and gas platform, as well as the scenario of a gas leak from riser pipeline of a floating production platform. The lessons learned were then applied to design an optimized QRA process for a real case pre-project assessment for a proposed addition of a riser platform to a fixed offshore oil and gas platform complex using Individual Risk per Annum (IRPA) and Potential Loss of Life (PLL) analyses. Findings reveal that applying the standard Hazard and Effects Management Process (HEMP) and As Low as Reasonably Practicable (ALARP) guidelines and tools alone are insufficient. The application of practical lessons learned from the past oil and gas disasters using IRPA and PLL parameters has helped this research to produce an optimized QRA. The optimized QRA process is a live process which could be further improved with future lessons learned.