That, along with new tyres with a slightly different overall diameter and even tyre pressures that havent been checked for a while, dirty engine air filter or even dirty fuel filters, are likely to be contributing factors.
On most cars the Mass Air Flow sensor (MAF) is used to estimate the fuel consumption.
The MAF measures how much air the engine is using and it knows that for every 14.7 grams of air, one gram of fuel is used.