You can generate this report if all data has been previously input properly to Leon (read this chapter for more information).
Once data is added to the Journey Log and there is enough flights with journey logs filled in with used oil data, you can view the average oil usage for all aircraft or per a particular tail.
You can see an example on the screenshot: for first several flights there is no oil usage data because for this particular aircraft there is Oil report period set as 50. That means, that there has to be a block of flights with at least 45:00 flight hours (as 10% offset off the value 50 hours is taken).
In the column Oil uplift you can see number of quarts inserted for each engine (taken from Journey Log). Then from the flight performed on 12-05-2015 you can see the average oil consumption based on the block of flights with total flight hours of at least 45.