When mixed with parenteral nutrients as an all-in-one admixture, previous data have demonstrated that lipid emulsions composed of medium-chain triglycerides (MCTs) and long-chain triglycerides (LCTs) yield more stable formulations compared with those compounded with pure LCT lipid emulsions. We investigated the physical stability of various preparations of intravenous lipid emulsions as all-in-one admixtures. Each final lipid emulsion used to compound the all-in-one formulation was a 20% w/v mixture containing MCTs and LCTs as either a single emulsion containing both triglycerides, or an emulsion made extemporaneously from separate starting emulsions of pure MCT and LCT. The first emulsion was composed of a 50:50 (by weight) physical mixture of MCTs and LCTs, and consisted of 50% MCT:40% omega-6 LCT (soybean oil):10% omega-3 LCT (fish oil) that was available as a single 20% w/v lipid emulsion. The second and third emulsions were specially prepared from separate stock dispersions containing pure 20% w/v MCT and pure 20% w/v LCT (soybean oil) lipid emulsions, and were made in volume ratios of 75% MCT:25% omega-6 LCT and 50% MCT:50% omega-6 LCT, respectively. This was done in order to investigate whether the method of emulsion preparation and/or ratio of MCT to LCT influenced all-in-one admixture stability. Each all-in-one admixture was studied at four intervals over 30 h at room temperature conditions by light extinction (or obscuration) using a single-particle optical sensing (LE/SPOS) technique. The data, performed in duplicate at each interval, is expressed as the volume-weighted percent of fat (PFAT) globules >5 microm. The results confirm the stabilizing effects of MCTs when made as a physical oil mixture as a single lipid emulsion. However, stabilization is lost if the MCT and LCT emulsions are mixed from separate starting emulsions and then compounded as an all-in-one formulation. The extemporaneous mixing of commercial lipid emulsions is not recommended.