Mutual funds that concentrate on the energy and natural resources sectors suffered a setback last month after sizeable increases in April, according to preliminary performace data released Tuesday by Toronto-based Morningstar Research Inc.

Twenty-eight of 42 fund Indices increased during the month, including seven that increased by 2% or more, Morningstar says, while three of the fund indices that lost ground decreased by more than 2%.

The energy equity fund index posted May’s worst result with a 5.6% decline, while the natural resources equity fund ondex posted May’s third-worst result with a 2.6% decline. Worldwide crude oil prices dropped in May, in large part because of a two-and-a-half year high in OPEC production.

The decline in energy had a large effect on funds in the Canadian equity category, where energy represents more than one-fifth of the holdings. The Canadian equity fund index was a poor performer in May, decreasing by 1%.

Recent economic data indicates that lower investment in Canada’s oil patch contributed to a 0.6% contraction in the Canadian economy during the first quarter of 2015, notes Morningstar. In addition, the Canadian dollar is down against currencies including the U.S. dollar, the British pound and the Chinese yuan.

Funds in the U.S. equity and U.S. small/mid cap equity categories, which were the worst performers in April, had a very different month in May, posting increases of 3.5% and 4.2%, respectively.

The S&P 500 Index of large-capitalization U.S. stocks was up 1.3% for the month, but for Canadian investors the more significant contributor was currency effect. The U.S. dollar rebounded by 2.9% versus its Canadian counterpart in May after a 4.4% decline in April, which was its worst monthly result since July 2009.

While recent reports indicate the U.S. economy saw its own contraction of 0.7% in the first quarter of 2015, few expect it to continue, with the end of both a tough winter and a labour dispute at West Coast ports, Morningstar notes.

The majority of the fund Indices that track foreign equity categories were up this month, except for the emerging markets equity fund index, which declined by 0.8%. The poor performance of Brazilian stocks contributed to the decline, along with the depreciation of the Brazilian real versus the Canadian dollar.

Final performance figures will be published next week.