Conagra Brands Inc. emerged as the best-performing stock in the S&P 500 Consumer Staples index in December 2019 following a strong second fiscal quarter that exceeded analysts' expectations, according to data compiled by S&P Global Market Intelligence.

The consumer staples sector recorded a 2.4% gain in December, versus a 1.3% gain in November 2019. Only six out of the 33 constituents of the index declined.

However, the sector fell behind the wider S&P 500 index, which recorded a gain of 3.0%, compared to its 3.6% advance in November.

Conagra topped the S&P 500 Consumer Staples index with an 18.6% gain in December after reporting an 8.3% year-over-year rise in adjusted diluted EPS for its fiscal second quarter. The maker of Hunt's tomato ketchup and Slim Jim jerky snacks grew net sales 18.3% during the quarter.

Agricultural company Archer-Daniels-Midland Co. was the second-best performer across the consumer staples sector, buoyed by the U.S. and China's latest trade agreement that calls for more purchases of agricultural products, among others, from the U.S. to China. ADM booked an 8.0% gain in December, up from 3.0% a month prior.

Colorado-based brewer Molson Coors Brewing Co. bounced back to the third-best spot in the index with an advance of 6.8% in December, compared to a 3.2% drop a month prior.

CoverGirl parent Coty Inc., whose shares dropped 0.2% in November, fell further in December with a 2.5% decline, placing it at the bottom of the S&P 500 Consumer Staples index.

The cosmetics company is in the midst of a four-year turnaround plan to improve its profitability and reduce debt. On Dec. 11, 2019, Coty announced that it appointed former Mars Inc. Vice President Pascal Baltussen as its global chief procurement officer, effective Jan. 1, to help the company's procurement team reduce complexity and costs.

Costco Wholesale Corp. was the second-worst performing stock in the consumer staples sector in December with a 2.0% drop, compared to a gain of 0.9% in November.

Despite beating analysts' expectations for its fiscal first quarter ended Nov. 24, 2019, Costco's stock fell after two of the retailer's executive vice presidents, Roland Vachris and Patrick Callans, sold a portion of their Costco holdings for a combined $2.4 million. Vachris sold $1.8 million worth of Costco stock Dec. 17, 2019, while Callans sold nearly $590,000 worth of his shares Dec. 26, 2019.

Drugstore chain Walgreens Boots Alliance Inc., the third-best performing consumer staples stock in November, was the third-worst performer in December with a 1.1% loss. It came as analysts forecast a year-over-year decline in Walgreens' EPS and net income for the fiscal first quarter ended November, according to data from Market Intelligence. The company is scheduled to release its results for the quarter Jan. 8. For the full 2020 fiscal year, Walgreens expects roughly flat growth in adjusted EPS.

Also during the month, Walgreens' stock fell to as low as $57.09 following a report by The Wall Street Journal on Dec. 1, 2019, that the drugstore chain's proposed take-private by buyout firm KKR & Co. Inc. has stalled. The newspaper, citing people familiar with the matter, said the two parties have failed to agree on the valuation of the deal.

Across the S&P 500, the energy sector was the best performer in December with a 6.0% gain. The S&P 500 Industrials index was the worst performer with a 0.1% loss, the only sector to record a decline.

Tech company Western Digital Corp. was the best-performing stock in the S&P 500 in December with a 26.1% return, while healthcare equipment maker Abiomed Inc. was the worst performer with a 13.0% loss.