Gross Margin, LIFO and FIFO Gross Margin
We define gross margin as sales minus merchandise costs, including advertising, warehousing, and transportation. Rent expense, depreciation and amortization expense, and interest expense are not included in gross margin.
Our gross margin rate, as a percentage of sales, was 21.66% for the third quarter of 2021, compared to 22.95% for the third quarter of 2020. The decrease in rate in the third quarter of 2021, compared to the third quarter of 2020, resulted primarily from increased fuel sales, which have a lower gross margin rate, a decrease in our fuel gross margin, continued investments in lower prices for our customers, a higher LIFO charge and increased transportation costs, as a percentage of sales, partially offset by effective negotiations to achieve savings on the cost of products sold.
Our gross margin rate, as a percentage of sales, was 21.96% for the first three quarters of 2021, compared to 23.44% for the first three quarters of 2020. The decrease in rate in the first three quarters of 2021, compared to the first three quarters of 2020, resulted primarily from increased fuel sales, which have a lower gross margin rate, a decrease in our fuel gross margin, continued investments in lower prices for our customers, a COVID-19-related inventory write down for personal protective equipment to be donated to community partners, the effect of supermarket sales deleverage, excluding fuel, due to cycling COVID-19 trends which decreases our gross margin, as a percentage of sales, a higher LIFO charge and increased shrink and transportation costs, as a percentage of sales, partially offset by growth in our alternative profit businesses and effective negotiations to achieve savings on the cost of products sold.
Our LIFO charge was $93 million for the third quarter of 2021 compared to $23 million for the third quarter of 2020. Our LIFO charge was $177 million for the first three quarters of 2021 compared to $77 million for the first three quarters of 2020. The increase in our LIFO charge reflects our expected annualized product cost inflation for 2021, compared to 2020, and was primarily driven by grocery and meat.
Our FIFO gross margin rate, which excludes the third quarter LIFO charge, was 21.95% for the third quarter of 2021, compared to 23.03% for the third quarter of 2020. Our fuel sales lower our FIFO gross margin rate due to the very low FIFO gross margin rate, as a percentage of sales, of fuel sales compared to non-fuel sales. Excluding the effect of fuel, our FIFO gross margin rate decreased 41 basis points in the third quarter of 2021, compared to the third quarter of 2020. This decrease resulted primarily from continued investments in lower prices for our customers and increased transportation costs, as a percentage of sales, partially offset by effective negotiations to achieve savings on the cost of products sold.
Our FIFO gross margin rate, which excludes the first three quarters LIFO charge, was 22.13% for the first three quarters of 2021, compared to 23.52% for the first three quarters of 2020. Excluding the effect of fuel, our FIFO gross margin rate decreased 57 basis points in the first three quarters of 2021, compared to the first three quarters of 2020. This decrease resulted primarily from continued investments in lower prices for our customers, a COVID-19-related inventory write down for personal protective equipment to be donated to community partners, the effect of supermarket sales deleverage, excluding fuel, due to cycling COVID-19 trends which decreases our gross margin, as a percentage of sales, and increased shrink and transportation costs, as a percentage of sales, partially offset by growth in our alternative profit businesses and effective negotiations to achieve savings on the cost of products sold.
Operating, General and Administrative Expenses
OG&A expenses consist primarily of employee-related costs such as wages, healthcare benefit costs, retirement plan costs, utilities, and credit card fees. Rent expense, depreciation and amortization expense, and interest expense are not included in OG&A.
OG&A expenses, as a percentage of sales, were 16.25% for the third quarter of 2021, compared to 17.48% for the third quarter of 2020. The decrease in the third quarter of 2021, compared to the third quarter of 2020 resulted primarily from the effect of increased sales to retail customers without fuel, which decreases our OG&A rate, as a percentage of sales, the 2020 Third Quarter OG&A Adjusted Items, the effect of increased fuel sales, which decreases our OG&A rate, as a percentage of sales, decreased incentive plan costs and broad-based improvement from cost savings initiatives that drive administrative efficiencies, store productivity and sourcing cost reductions, partially offset by investments in hourly rate and benefits for our associates and the 2021 Third Quarter OG&A Adjusted Items.