A grease delivery system for delivering grease to a well intervention unit, comprising: first and second grease reservoirs, a first grease reservoir output for outputting grease from the first reservoir, a second grease reservoir output for outputting grease from the second reservoir, and respective means for causing grease to output from each of said first and second reservoirs along the respective grease reservoir output, wherein the system further comprises a common grease output for delivering grease to the well intervention unit, the common grease output being connected to each of the first and second grease outputs, such that grease may be output simultaneously from the first and second reservoirs to the common grease output, wherein each respective means for causing grease to output from said respective reservoirs comprises a hydraulic fluid supply means for supplying hydraulic fluid to each of the respective reservoirs, to displace grease therefrom, wherein the hydraulic fluid supply means comprises a hydraulic fluid valve (2, 2', 13, 13') associated with each of the reservoirs (3, 3'), the valves being operable to selectively enable hydraulic fluid flow therethrough to the respective reservoir, characterised in that each hydraulic fluid valve (13, 13') is hydraulically-piloted or is ROV-operable, wherein the grease delivery system further comprises a grease valve (9, 9', 14, 14') located in each grease reservoir output being operable to selectively allow or block grease flow therethrough, wherein each grease valve (9, 9') is hydraulically-piloted or is ROV-operable, wherein each reservoir includes sensing means for sensing the level of grease within the reservoir, and wherein the hydraulic fluid valves, grease valves, and sensing means are configured to simultaneously supply grease to the common grease output from both grease reservoirs to ensure a seamless supply of grease until a) the grease level of one grease reservoir is exhausted as detected by the sensing means, or b) the grease level of one grease reservoir reaches a pre-set lower limit as detected by the sensing means, or c) after a pre-set length of time. first and second grease reservoirs, a first grease reservoir output for outputting grease from the first reservoir, a second grease reservoir output for outputting grease from the second reservoir, and respective means for causing grease to output from each of said first and second reservoirs along the respective grease reservoir output, wherein the system further comprises a common grease output for delivering grease to the well intervention unit, the common grease output being connected to each of the first and second grease outputs, such that grease may be output simultaneously from the first and second reservoirs to the common grease output, wherein each respective means for causing grease to output from said respective reservoirs comprises a hydraulic fluid supply means for supplying hydraulic fluid to each of the respective reservoirs, to displace grease therefrom, wherein the hydraulic fluid supply means comprises a hydraulic fluid valve (2, 2', 13, 13') associated with each of the reservoirs (3, 3'), the valves being operable to selectively enable hydraulic fluid flow therethrough to the respective reservoir, characterised in that each hydraulic fluid valve (13, 13') is hydraulically-piloted or is ROV-operable, wherein the grease delivery system further comprises a grease valve (9, 9', 14, 14') located in each grease reservoir output being operable to selectively allow or block grease flow therethrough, wherein each grease valve (9, 9') is hydraulically-piloted or is ROV-operable, wherein each reservoir includes sensing means for sensing the level of grease within the reservoir, and wherein the hydraulic fluid valves, grease valves, and sensing means are configured to simultaneously supply grease to the common grease output from both grease reservoirs to ensure a seamless supply of grease until a) the grease level of one grease reservoir is exhausted as detected by the sensing means, or b) the grease level of one grease reservoir reaches a pre-set lower limit as detected by the sensing means, or c) after a pre-set length of time. a) the grease level of one grease reservoir is exhausted as detected by the sensing means, or b) the grease level of one grease reservoir reaches a pre-set lower limit as detected by the sensing means, or c) after a pre-set length of time.