Lubricant for horizontal wells shall be applied in mud for increasing their lubricating properties during the performance of drilling procedures. A good lubricating property of drilling mud is very important for a considerable time-saving, prolongation of equipment durability, reduction of the number of manoeuvres, and more cost-effective operation of the entire drilling procedure. Pollution of the environment (soil and water) is preventable by applying environmentally more advatageous raw materials in lubricants. Rapeseed oils belongs to a group of base oils acceptable for the environment, so, in addition to an easy and relatively fast biodegradation it has also other advantageous properties as good lubricity, high viscosity, good adhesiveness to metal surfaces, and very good loadcarrying properties. It is possible to improve poor application properties of rapeseed oil: behaviour at high and low temperatures, hidrolytic stability, as well as foaming property, by admixing suitable additives.