Looking up some old notes I had from around 1984,
excise duty was calculated from gravity degrees,
1 barrel(36 gallons),@ 1055; £140.55 (€178.50),
sample 1 barrel(36 gallons) @ 1038; £97.11 (€123.33),
gross revenue per barrel; £173.64 (€220.52),
revenue less excise per barrel; £76.53 (€97.19),
electricity per barrel; £4.836 (€6.14),
L.P.G. per barrel; £3.255 (€4.133).