Net sales for the Strategic Brands segment were $67.8 million for the three-months ended March 31, 2021, an increase of approximately $3.3 million, or 5.1% higher than net sales of $64.5 million for the three-months ended March 31, 2020. Net sales for the Strategic Brands segment increased primarily due to increased worldwide sales by volume of our Predator® and Mother® brand energy drinks as a result of increased consumer demand. Net changes in foreign currency exchange rates had no significant impact on net sales for the Strategic Brands segment for the three-months ended March 31, 2021.
Net sales for the Other segment were $5.7 million for the three-months ended March 31, 2021, an increase of approximately $0.6 million, or 12.2% higher than net sales of $5.1 million for the three-months ended March 31, 2020.
Case sales, in 192-ounce case equivalents, were 138.6 million cases for the three-months ended March 31, 2021, an increase of approximately 23.0 million cases or 19.9% higher than case sales of 115.6 million cases for the three-months ended March 31, 2020. The overall average net sales per case (excluding net sales of AFF Third-Party Products of $5.7 million and $5.1 million for the three-months ended March 31, 2021 and 2020, respectively, as these sales do not have unit case equivalents) decreased to $8.94 for the three-months ended March 31, 2021, which was 2.3% lower than the average net sales per case of $9.14 for the three-months ended March 31, 2020. The decrease in the average net sales per case was primarily the result of geographical sales mix and higher promotional allowances as a percentage of net sales.
Gross Profit. Gross profit was $714.9 million for the three-months ended March 31, 2021, an increase of approximately $77.7 million, or 12.2% higher than the gross profit of $637.2 million for the three-months ended March 31, 2020. The increase in gross profit dollars was primarily the result of the $181.7 million increase in net sales for the three-months ended March 31, 2021.
Gross profit as a percentage of net sales decreased to 57.5% for the three-months ended March 31, 2021 from 60.0% for the three-months ended March 31, 2020. The decrease for the three-months ended March 31, 2021 was primarily the result of increased input costs (mainly increased raw material freight-in costs), geographical sales mix, and higher promotional allowances as a percentage of net sales.
Operating Expenses. Total operating expenses were $300.8 million for the three-months ended March 31, 2021, an increase of approximately $28.6 million, or 10.5% higher than total operating expenses of $272.2 million for the three-months ended March 31, 2020. As a percentage of net sales, operating expenses for the three-months ended March 31, 2021 were 24.2% as compared to 25.6% for the three-months ended March 31, 2020. The increase in operating expenses was primarily due to increased out-bound freight and warehouse costs of $15.6 million, increased payroll expenses of $13.7 million (of which $0.9 million was related to an increase in stock-based compensation), increased expenditures of $6.1 million for social media and digital marketing, and increased expenditures of $4.2 million for professional service expenses, including accounting and legal costs. The increase in operating expenses was partially offset by decreased expenditures of $5.8 million for travel and entertainment largely as a consequence of the COVID-19 pandemic.
Operating Income. Operating income was $414.1 million for the three-months ended March 31, 2021, an increase of approximately $49.2 million, or 13.5% higher than operating income of $365.0 million for the three-months ended March 31, 2020. Operating income as a percentage of net sales decreased to 33.3% for the three-months ended March 31, 2021 from 34.4% for the three-months ended March 31, 2020. Operating income was $92.1 million and $71.7 million for the three-months ended March 31, 2021 and 2020, respectively, for our operations in EMEA, Asia Pacific and South America.
Operating income for the Monster Energy® Drinks segment, exclusive of corporate and unallocated expenses, was $464.8 million for the three-months ended March 31, 2021, an increase of approximately $53.7 million, or 13.1% higher than operating income of $411.1 million for the three-months ended March 31, 2020. The increase in operating income for the Monster Energy® Drinks segment was primarily the result of the $177.8 million increase in net sales for the three-months ended March 31, 2021.
Operating income for the Strategic Brands segment, exclusive of corporate and unallocated expenses, was $45.1 million for the three-months ended March 31, 2021, an increase of approximately $8.4 million, or 22.9% higher than operating income of $36.7 million for the three-months ended March 31, 2020. The increase in operating income for the Strategic Brands segment was primarily the result of the $3.3 million increase in net sales as well as a $3.0 million Strategic Brand trademark impairment charge that was recorded in the comparative 2020 first quarter.
Operating income for the Other segment, exclusive of corporate and unallocated expenses, was $1.8 million for the three-months ended March 31, 2021, an increase of approximately $1.0 million, or 128.0% higher than operating income of $0.8 million for the three-months ended March 31, 2020.