By Paul Hannon 

The eurozone was still mired in deflation during May, and while economists expect consumer prices to start rising in coming months, success for the European Central Bank in meeting its inflation target is far from assured.

The European Union's statistics agency on Tuesday said consumer prices were 0.1% lower than in May 2016, the second straight month of deflation in the currency area.

That's a frustrating outcome for ECB policy makers, who have launched a series of stimulus packages since mid-2014 with the aim of raising inflation to their target of just under 2%, the most recent coming in March.

Inflation has been below the ECB's target for more than three years, including two years over which it has been at 0.5% or lower. Since December 2014, the eurozone has been in deflation for eight months, including May.

However, rising oil prices point to a pickup in inflation during the second half of this year, and the ECB's economists are expected to raise their inflation forecasts Thursday, a rare occurrence in recent years.

Economists at Standard & Poor's estimate that oil prices are 30% higher than the ECB's assumptions for 2016 and up 75% from the trough reached in late January of this year.

Inflation may receive an additional boost if the U.S. Federal Reserve were to raise its short-term interest rates over coming months, since that would likely weaken the euro and raise prices of imported goods and services.

There are also signs that the ECB's efforts to boost bank lending are having some success. Figures it released Tuesday showed lending to the private sector was 1.2% higher in April than a year earlier, compared with growth of 1.1% in March, although lending to households slowed.

However, the ECB's ability to meet its inflation target will ultimately depend on the strength of economic growth within the eurozone, and that is likely to remain weak.

Inflation has been extremely low for so long in part because of the modest nature of the eurozone's recovery, with the economy only returning to its precrisis size in the first three months of this year.

Eurostat's figures showed that excluding items such as food and energy, the prices of which are set mainly in world markets, the core rate of inflation was just 0.8%, a pickup from 0.7% in April.

While the eurozone economy had a stronger first quarter than either the U.S. or the U.K., economists expect to see a slowdown in this and subsequent quarters, leaving growth for 2016 roughly in line with a disappointing 2015.

Figures also released Tuesday by Eurostat showed the jobless rate was unchanged from March at 10.2% in April, although there were 63,000 fewer people without jobs. That left the eurozone with an unemployment rate more than double that of the U.S., leaving consumer demand weaker and businesses more reluctant to raise their prices.

Despite the improved outlook, ECB economists are expected to continue to forecast that inflation will remain below target in 2018. The ECB's governing council is expected to leave policy unchanged when it meets Wednesday and Thursday, but ECB President Mario Draghi will likely signal that further stimulus measures are a possibility if inflation doesn't pick up decisively later this year.

Todd Buell contributed to this article.

Write to Paul Hannon at paul.hannon@wsj.com

(END) Dow Jones Newswires

May 31, 2016 05:32 ET (09:32 GMT)

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