Here's why Opec's global oil cuts might result in sharp price spikes

The group's spare capacity has ballooned to about 3.4 million barrels a day, as of November, compared with about 2 million a day at the outset of the production curbs

The unintended consequence of the Organization of Petroleum Exporting Countries or Opec's quest to drain a global oil glut may be a sharp rise in price volatility as the buffer against worldwide turmoil and disruptions is stripped back.

Due to the glut, suicide bombers in the Iranian capital, independence efforts by Iraq's Kurdistan region, and war in Syria and Yemen are among a number of flareups in, or near, key producing regions in the past few years that barely registered on oil markets. In some cases, prices fell when they would previously have jumped.

Now, Citigroup Inc. is predicting a