Reservoir capacity has been reduced for both petrol engines (from 68.3 to 67.4 liters) and diesel (54.2 to 53.7 liters). The presence or lack of an energy recovery system has no bearing on the fuel tank capacity, unlike the amount of energy allotted per lap.
Indeed, the more one recovers energy, the less one can burn fuel during a lap, which allows a balance to be reached in the performances. For example Porsche, in the highest energy recovery category (8 megajoules), is allowed less fuel per lap than Toyota, who opted for the 6 megajoules category. Therefore, the additional power provided by the Porsche hybrid system is supposed to be balanced by a higher energy allowance for Toyota.
Energy allowances were generally decreased for fuel engine prototypes, whereas diesel prototypes like Audi (4 megajoules) will benefit from a slight boost if they figure within the two lowest recovery categories (2 to 4 MJ), but those in the two highest categories will have to make due with less energy 6 to 8 MJ).
This table shows only the energy values valid at the 24 Hours of Le Mans in 2016. The tables related to the other FIA World Endurance Championship (WEC) races are available by clicking the link.

Cécile Bonardel / ACO - Translation by Nikki Ehrhardt / ACO
PHOTO: LE MANS (SARTHE, FRANCE), CIRCUIT DES 24 HEURES, 24 HOURS OF LE MANS, WEDNESDAY JUNE 10 2015, QUALIFYING. The amount of energy granted to the Porsche 919 Hybrid and the Audi R18 e-tron quattro has been revised.