India, July 29 -- At a bar in New Delhi in May, guests in Diet Coke-themed T-shirts queued up for cocktails spiked with jalapeno and honey and painted cans as party activities. In Mumbai, a similar ticketed evening ended in a raffle whose top prize was 50 cans of the drink itself. Near the capital, a restaurant chain was charging Rs.1,300 for entry to an evening that promised the fizzy drink "on the house" alongside snacks, while a separate retail chain in New Delhi was billing its own Rs.999 event - with burgers, vintage art and custom T-shirt painting - as a "full-blown Diet Coke experience".

The parties were a response to a very real problem: Diet Coke, sold almost exclusively in aluminium cans in India, has been in short supply for m...