The ever pressing demand to increase the output from a given size of equipment causes the requirements made on lubrication arrangements to be progressively more arduous. This situation creates the need for improvements to arrangements which have in the past been satisfactory but now are not capable of meeting the present day demands. This article gives details of experimental work carried out during the development of an improved self‐contained oil lubrication arrangement for rolling bearings with horizontal rotating shaft. This arrangement has been given the trade mark CIRCON and has been used successfully for light series bearings operating at speed factors up to 420,000 mm/min. It is based on the Oil Bath arrangements which due to its simplicity has been adopted for a variety of applications over many years. In spite of this, little information is available on its performance and on its limitations. It was therefore necessary to study the operation of the basic oil bath arrangements in order to judge what improvements could be made.