Tractor Vaporising Oil (TVO) can be mixed using petrol and heating oil.  FOFH give some good guidance on mixing TVO.  This is the method and ingredients they recommend….

There must only ever be 2 ingredients in TVO1. Petrol (unleaded is absolutely fine for a Ferguson tractor) 98 Octane.
2. 28 Second Heating Oil 20 Octane.

Aim for an Octane value between 55 and 70.

55 if doing very hard work
70 if doing topping and the like

To give you some idea of the sums:-

1 part petrol and 1 part heating oil comes out at 59 Octane.
2 parts petrol and 1 part heating oil comes out at 72 Octane.
1 part petrol and 2 parts heating oil comes out at 46 Octane.
Petrol on its own is suitable for road runs (with the heat shield removed).

Octane is not the only factor, but it provides a good guide.

Diesel fuel is designed to cause ignition by compression and will encourage pinking. It is not designed to burn in TVO tractors, and no upper cylinder lubricant is required in these tractors, so do not use anything other than petrol and heating oil.

Using fuel which does not burn completely will destroy the lubricating properties of the oil and that (in a Ferguson TE tractor) will result in wear to the cam shaft bushes and then loss of oil pressure from cam shaft bushes. Loss of oil pressure will, then result in damage to the crank shaft. Lubricating oil in a TVO tractor’s engine should be changed according to the Tractor Instruction book.

Ferguson FE35 thermostat, jet information and identifying if your tractor is a VO or Lamp Oil version.

How to get a good mix of TVO.