European stock markets and Wall Street all reversed earlier losses to trade higher, but the gains were small, indicating traders remain cautious.
One of the most notable movements was in the Mexican peso  which surged to a two-month high against the US dollar.
The currency's rise suggests investors expect Donald Trump to lose.
Mexico is expected to suffer should Mr Trump be elected because of his pledges to build a wall along the US border with the country and renegotiate their trade agreement.
In Europe, London's FTSE 100 and stock markets in Paris and Frankfurt all made small gains of between 0.2% and 0.5%, while in the US the three main stock indexes jumped between 0.4% to 0.5%.
Analysts said the number of shares being traded was lower than normal, indicating investors are still uncertain about the result.
"2016 has been a year full of surprises. Don't forget the markets priced in a Remain win in the Brexit referendum and got it wrong," said Nigel Green, chief executive of deVere Group.
He warned a victory for Mr Trump could deliver a "double whammy negative impact" on global markets because they are expecting Mrs Clinton to win.
"Should she win, global financial markets will react favourably as she is seen to represent the status quo, whereas Trump is much more of an unknown and therefore will create uncertainty and the markets will react accordingly," he said.
Major banks have told clients to expect sharp movements in currency markets, and are reported to have put extra staff on duty throughout the night.
The cost of protecting against sharp movements in currencies such as the Mexican peso and the US dollar rose suggesting investors were expecting volatility as the results come in.
"It doesn't take much in order to move the prices," said Peter Jankovskis, co-chief investment officer at OakBrook Investments.
Stock markets around the world have risen slightly and the Mexican peso has surged suggesting traders are betting on a Clinton victory.