The State Street Investor Confidence Index (ICI) rose to 108.3 in December, up one point from November's revised reading of 107.3.
The index takes a reading of 100 as 'neutral' on institutional investors' appetite for risky assets.
European sentiment increased from 96.2 to 103.7 in December, while the Asian ICI was up 4.6 points to 105.1.
The North American ICI, by contrast, decreased 5.9 points to 106.6.
State Street Associates' Kenneth Froot, who developed the ICI with his colleague Paul O'Connell, said US investors have become "increasingly risk averse" into the year end.
"Uncertainty about global growth, weak commodity prices and the beginning of the Fed tightening cycle have eroded confidence to take risk," Mr Froot said.
Senior managing director and head of global macro strategy at State Street Global Markets, Michael Metcalfe said, "The knee-jerk reaction from European equity and bond markets was to sell off together when the European Central Bank eased but failed to increase its asset purchases program in early December.
"It appears European long-term investors were more forgiving as their allocation to risky assets went up over the course of the month," Mr Metcalfe said.