Electrical Oil Services Ltd (EOS) is a joint venture company and came into being on 01 November 1999. EOS was formed by the amalgamation of the electrical oils businesses of Castrol (UK) Ltd and Carless Refining & Marketing Ltd, who were the UK's leading suppliers of insulating oils and associated services to the electricity supply industry, the electrical engineering industry, and energy-intensive, high voltage, industrial electricity users.

The establishment of EOS as a stand-alone operation, concentrating solely on the electrical oils business, means that our structure and systems can be dedicated to meeting the specific needs of our customer base. Operations are based at the former Castrol electrical oils plant at Stanlow, near Ellesmere Port, Cheshire. This is the hub of our activities where the business functions of sales, administration and accounts are handled. In addition to being the central storage point for the distribution of unused mineral insulating oils, Stanlow is home to the UK's only dedicated plant for the reclamation of used insulating oils to as-new (BS148: 1998) condition. Additional services such as on-site, in-situ, oil reconditioning (purifying) plants known as Mobile Processing Units (MPUs), and the TransTest oil analysis service are also operated from Stanlow.