Proponents say a pension obligation bond, or POB, would ease fiscal pressure as the city confronts a $1.2 billion budget gap, $31 billion in unfunded pension liabilities and a projected $756 million increase in required annual pension contributions over the next six years. Critics warn that POBs have worsened fiscal problems for other cities and raise the specter of former Illinois Gov. Rod Blagojevich’s ill-fated POB, which failed to solve the state’s pension problems.