Case sales, in 192-ounce case equivalents, were 460.0 million cases for the nine-months ended September 30, 2021, an increase of approximately 87.5 million cases or 23.5% higher than case sales of 372.5 million cases for the nine-months ended September 30, 2020. The overall average net sales per case (excluding net sales of AFF Third-Party Products of $20.0 million and $20.4 million for the nine-months ended September 30, 2021 and 2020, respectively, as these sales do not have unit case equivalents) decreased to $8.91 for the nine-months ended September 30, 2021, which was 1.9% lower than the average net sales per case of $9.08 for the nine-months ended September 30, 2020. The decrease in the average net sales per case was primarily the result of geographical sales mix.
Gross Profit. Gross profit was $2.34 billion for the nine-months ended September 30, 2021, an increase of approximately $307.7 million, or 15.1% higher than the gross profit of $2.03 billion for the nine-months ended September 30, 2020. The increase in gross profit dollars was primarily the result of the $714.0 million increase in net sales for the nine-months ended September 30, 2021.
Gross profit as a percentage of net sales decreased to 56.9% for the nine-months ended September 30, 2021 from 59.8% for the nine-months ended September 30, 2020. The decrease for the nine-months ended September 30, 2021 was primarily the result of increased aluminum can costs attributable to higher aluminum commodity pricing, as well as the costs of importing aluminum cans, logistical costs and geographical sales mix.
Operating Expenses. Total operating expenses were $956.3 million for the nine-months ended September 30, 2021, an increase of approximately $154.0 million, or 19.2% higher than total operating expenses of $802.3 million for the nine-months ended September 30, 2020. As a percentage of net sales, operating expenses for the nine-months ended September 30, 2021 were 23.2% as compared to 23.6% for the nine-months ended September 30, 2020. The increase in operating expenses was primarily due to increased out-bound freight and warehouse costs of $63.3 million, increased payroll expenses of $30.6 million, increased expenditures of $27.2 million for sponsorships and endorsements, increased expenditures of $14.1 million for social media and digital marketing, and increased expenditures of $10.6 million for professional service expenses, including accounting and legal costs. The increase in operating expenses for the nine-months ended September 30, 2021, was partially offset by $16.9 million due to the reversal of amounts previously accrued in connection with an intellectual property claim.
Operating Income. Operating income was $1.38 billion for the nine-months ended September 30, 2021, an increase of approximately $153.7 million, or 12.5% higher than operating income of $1.23 billion for the nine-months ended September 30, 2020. Operating income as a percentage of net sales decreased to 33.6% for the nine-months ended September 30, 2021 from 36.2% for the nine-months ended September 30, 2020. Operating income was $325.8 million and $237.3 million for the nine-months ended September 30, 2021 and 2020, respectively, for our operations in EMEA, Asia Pacific, Latin America and the Caribbean.
Operating income for the Monster Energy® Drinks segment, exclusive of corporate and unallocated expenses, was $1.51 billion for the nine-months ended September 30, 2021, an increase of approximately $145.7 million, or 10.7% higher than operating income of $1.37 billion for the nine-months ended September 30, 2020. The increase in operating income for the Monster Energy® Drinks segment was primarily the result of the $683.6 million increase in net sales for the nine-months ended September 30, 2021.
Operating income for the Strategic Brands segment, exclusive of corporate and unallocated expenses, was $139.4 million for the nine-months ended September 30, 2021, an increase of approximately $21.1 million, or 17.8% higher than operating income of $118.3 million for the nine-months ended September 30, 2020. The increase in operating income for the Strategic Brands segment was primarily the result of the $30.8 million increase in net sales.
Operating income for the Other segment, exclusive of corporate and unallocated expenses, was $5.3 million for the nine-months ended September 30, 2021, an increase of approximately $0.5 million, or 10.1% higher than operating income of $4.8 million for the nine-months ended September 30, 2020.
Interest and Other Expense, net. Interest and other non-operating expense, net, was $2.2 million for the nine-months ended September 30, 2021, as compared to interest and other non-operating expense, net, of $5.5 million for the nine-months ended September 30, 2020. Foreign currency transaction losses were $5.5 million and $9.2 million for the nine-months ended September 30, 2021 and 2020, respectively. Interest income was $3.1 million and $6.9 million for the nine-months ended September 30, 2021 and 2020, respectively.