It is believed Tangye type "P" Petroleum (Oil) engines followed on from the previous non designated types that had followed on from the Pinkney's Patents engines.
As with most Tangye dating records when the first "P" engine was built is unknown, but from catalogues available the Type "P" engines were first listed in 1904.
As can be seen from the tables below, type "P" oil engines were given a two letter Reference designation, the first starting with the letter A then B etc, indicated engine HP then the second letter always P indicated type "P" Petroleum (Oil). Heavier flywheel Electric Light engines were given a third letter "E".
At or about the same time Type "B" Benzoline and Type "A" Alcohol engines were released.
I believe that the type "P" engines carried a Tangyes Patents plate that can be seen on Tangye Plates Page
This information was taken from "Oil Engines, Benzoline Engines, Alcohol Engines catalogue No 65 dated 1904.
As additional data is obtained the details on this page will be updated.
Note: Indicated HP is the theoretical power of a reciprocating engine and is completely frictionless. It is calculated from the pressures developed in the cylinders.
Effective HP is the truer HP rating taking into account engine losses such as friction and windage etc