Across Asia, the lowest crude prices since 2009 are an almost unmitigated boon. Already, they've given Indonesia and Malaysia room to curb budget-busting fuel subsidies (although Malaysia, an energy exporter, will suffer from a drop in oil revenues). In Japan, the Philippines, Singapore, South Korea, Taiwan and Thailand, sliding energy costs stand to boost disposable incomes, household demand and corporate profits. Economist Glenn Maguire at Australia & New Zealand Banking Group thinks this "confidence multiplier" will lead to higher-than-expected growth. The drop in oil prices so far could add as much as 1 percentage point to global output. "We think this will be the defining, constructive dynamic that underpins Asian growth in 2015 and most probably 2016," Maguire says.

As India's Modi prepares to unveil his first full budget in February, he could hardly ask for a fairer tailwind. In the short run, says Peter Redward, principal at Redward Associates, oil trends will lead to a "massive improvement" in India's current account deficit, repair the government's balance sheet and restrain inflation, which should allow the central bank to cut rates.

Whether the pickup in growth can be sustained will depend on how bold Modi chooses to be next year. The Indian prime minister wisely slashed diesel subsidies when oil prices dropped, easing the hit consumers felt at the pump. But that was the easy part; it’ll be tougher to cut subsidies on liquefied petroleum gas and kerosene, which millions of Indians use for cooking. Together with diesel, subsidies for those two fuels cost the government $11 billion in the last fiscal year. Likewise, Modi will have to spend considerable political capital to abandon discounts on fertilizer. Without such cuts, it'll be difficult to free up space for more productive fiscal spending on infrastructure, education and health care. 

Nor can Modi afford to delay supply-side reforms. In addition to lower fuel bills, 2015 will feature a light election calendar: Only two of India’s 29 states will hold contests. This could well be the prime minister's best chance to push through politically difficult measures, such as allowing foreigners to hold majority stakes in key domestic sectors.

David Fuller's view

Modi is ambitious, experienced and far more economically savvy than the head of government in most other countries, developed or undeveloped.  He also has an overall majority and a responsible central banker, so I do not think he needs our advice on how to run India’s economy. 

All politicians need an element of luck, and considerably lower oil prices are a huge benefit for all countries which import most of their energy.  Luck has favoured them, although today’s prices for crude oil are in reality, a triumph for US technology.  Modi would also benefit considerably from a good monsoon, which he did not get in 2014.  However, this is in the hands of the weather gods.