The eurozone tumbled into deflation in December as annual consumer prices slipped into negative territory on falling oil prices and weak demand.Annual inflation in the currency bloc slowed to a lower-than-forecast minus 0.2 per cent last month from 0.3 per cent in November, the EU's statistics office Eurostat said in preliminary data released on Wednesday.This is the first drop to negative territory since 2009.The slide is likely to add to market expectations that the European Central Bank will unveil in the coming months an ambitious program of government bond buying and private asset purchases aimed at boosting growth and reverse the downward inflationary spiral.Analysts surveyed by DPA-AFX had expected consumer prices to slip to minus 0.1 per cent last month after a 50-per-cent plunge in oil prices since the middle of the year and hesitant growth in the eurozone.