Warehouse club retailer Costco Wholesale (COST -0.15%) released its fiscal fourth-quarter and full-year results yesterday after market close, delivering several positive surprises. Riding the tailwinds of COVID-19's effects, rather than sustaining damage from them, Costco outperformed on a year-over-year basis.

Costco's earnings per share for Q4 amounted to a diluted $3.13 per share, 9.8% higher than the $2.85 analyst estimate reported by Zacks Equity Research. Revenue for the quarter also beat analyst predictions, coming in 1.75% ahead of the Wall Street figure of $53.38 billion.

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Image source: Getty Images.

In full-year terms, Costco also outstripped its previous-year performance. Diluted EPS rose 9.2% from $8.26 in fiscal year 2019 to $9.02 in fiscal 2020. Net sales, or revenue, closely traced these gains, surging 9.3% from $149.35 billion to $163.22 billion.

Adjusted comparable sales, or comps, also increased sharply for both Q4, at 14.1% year over year, and full-year fiscal 2020, at 9.2% year over year. E-commerce, predictably, skyrocketed too, soaring 91.3% for the quarter and 50.1% for the year. The coronavirus pandemic was a mixed blessing for the retailer's bottom line, however. The company racked up $281 million in pre-tax Q4 expenses in "premium wages and sanitation costs."

While the figures are quite positive, the durability of Costco's gains depends in part on its success in attracting subscribers and retaining them long-term. According to CFO Richard Galanti during the Q4 conference call, renewal rates remained steady at a robust 91% and membership fee income edged upward by $56 million, while paid members grew by 1.3 million -- overall upbeat figures for investors.