The bioavailability of long-chain omega-3 fatty acids is a critical yet often overlooked factor influencing their efficacy. This review evaluates the bioavailability of EPA/DHA from acute (single-dose) and chronic human studies, focusing on (a) chemical forms such as triacylglycerols (TAG, natural and re-esterified, rTAG), non-esterified fatty acids (NEFA), and phospholipids (PL) from sources like fish, krill, and microalgae, and (b) delivery methods like microencapsulation and emulsification. Bioavailability for isolated chemically forms followed the order: NEFA > PL > rTAG > unmodified TAG > ethyl esters (EE). However, varying oil compositions complicate conclusions about source-specific bioavailability. Significant differences observed in acute bioavailability studies (e.g., faster absorption) often did not translate into long-term impacts in chronic supplementation studies. This raises questions about the clinical relevance of acute findings, especially given that n-3 PUFA supplements are typically consumed long-term. Methodological limitations, such as inappropriate biomarkers, short sampling windows, and inadequate product characterization, hinder the reliability and comparability of studies. The review emphasizes the need for standardized protocols and robust chronic studies to clarify the clinical implications of bioavailability differences. Future research should prioritize biomarkers that reflect sustained n-3 PUFA status to better understand the health benefits of various EPA and DHA formulations.