Sentiment also was brightened by hopes that China and the U.S. are moving to ease trade tensions.
Germany's DAX edged 0.2% higher to 12,378 and the FTSE 100 in London was up less than 0.1% to 7,339. The CAC 40 in Paris was flat at 5,615. Wall Street appeared set for small gains, with the Dow futures up 0.2% and those for the S&P up 0.1%.
Analysts say the ECB is likely to cut a key interest rate further below zero on Thursday and could take other steps, including restarting a bond-buying program to pump newly created money into the economy.
In Asia, investors also drew encouragement from China's decision to exempt some U.S. products from a recent round of tariffs.
Tokyo's Nikkei 225 index gained 0.8% to 21,759.61 while the Shanghai Composite index also added 0.8% to 3,031.24. Australia's S&P ASX 200 climbed 0.3%, to 6,654.90. Hong Kong's Hang Seng index slipped 0.3% to end at 27,087.63.
An escalation in the trade war roiled financial markets this summer as investors fretted that higher tariffs and a slowing global economy could tip the U.S. into a recession. The economic uncertainty has also become a drag on companies.
Some of those trade concerns appeared to ease Wednesday after China said it will exempt American industrial grease and some other imports from tariff increases, though it kept in place penalties on soybeans and other major U.S. exports ahead of negotiations next month.
As a gesture of "goodwill," President Donald Trump said on Twitter that the United States agreed to a two-week delay in a planned increase in tariffs on some Chinese imports.
The moves could indicate that both sides are settling in for an extended conflict even as they prepare for talks in Washington aimed at ending the dispute that threatens global economic growth.
Still, the uncertainties appear likely to persist.
"Just as the presidential tweet on tariffs this morning has injected more momentum into stocks and most likely emerging-market assets, what one hand gives, the other can take away. We are only one social media posting away from a thoroughly unpredictable President turning sentiment on its head," Jeffrey Halley of Oanda said in a commentary.
Investors continue to expect the Federal Reserve will cut interest rates at its meeting next week in another bid by the central bank to help maintain U.S. economic growth. The Fed raised its benchmark interest rate in July by a quarter point. That was its first hike in a decade.
ENERGY: Benchmark crude oil lost 45 cents to $55.30 per barrel in electronic trading on the New York Mercantile Exchange. It fell $1.65 to settle at $55.75 a barrel on Wednesday. Brent crude oil, the international standard, gave up 70 cents to $60.11 per barrel. It dropped $1.57 to close at $60.81 a barrel overnight.
CURRENCIES: The dollar rose to 107.87 Japanese yen from 107.82 yen on Wednesday. The euro strengthened to $1.1023 from $1.1010.