Our FIFO gross margin rate, which excludes the first three quarters LIFO charge, was 23.52% for the first three quarters of 2020, compared to 22.14% for the first three quarters of 2019. Excluding the effect of fuel, our FIFO gross margin rate increased 20 basis points in the first three quarters of 2020, compared to the first three quarters of 2019. This increase resulted primarily from growth in our alternative profit stream portfolio, effective negotiations to achieve savings on the cost of products sold and decreased shrink, transportation and advertising costs, as a percentage of sales, reflecting the significant increase in sales volumes, partially offset by continued investments in lower prices for our customers and a change in our product sales mix, including lower relative sales in higher gross margin categories such as deli/bakery.
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 17.48% for the third quarter of 2020, compared to 18.23% for the third quarter of 2019. The decrease in the third quarter of 2020, compared to the third quarter of 2019 resulted primarily from the effect of increased sales due to the pandemic which decreases our OG&A rate, as a percentage of sales, the 2019 Third Quarter OG&A Adjusted Items and broad based improvement of Restock Kroger cost savings initiatives that drive administrative efficiencies, store productivity and sourcing cost reductions, partially offset by the 2020 Third Quarter OG&A Adjusted Items, the COVID-19 Investments, growth in our digital channel as a result of heightened demand during the pandemic, increased incentive plan costs and the effect of decreased fuel sales, which increases our OG&A rate, as a percentage of sales.
Our fuel sales lower our OG&A rate, as a percentage of sales, due to the very low OG&A rate, as a percentage of sales, of fuel sales compared to non-fuel sales. Excluding the effect of fuel, the 2020 Third Quarter OG&A Adjusted Items and the 2019 Third Quarter OG&A Adjusted Items, our OG&A rate decreased 30 basis points in the third quarter of 2020, compared to the third quarter of 2019. This decrease resulted primarily from the effect of increased sales due to the pandemic which decreases our OG&A rate, as a percentage of sales, and broad based improvement of Restock Kroger cost savings initiatives that drive administrative efficiencies, store productivity and sourcing cost reductions, partially offset by the COVID-19 Investments, growth in our digital channel as a result of heightened demand during the pandemic and increased incentive plan costs.
OG&A expenses, as a percentage of sales, were 17.85% for the first three quarters of 2020, compared to 17.37% for the first three quarters of 2019. The increase in the first three quarters of 2020, compared to the first three quarters of 2019 resulted primarily from the 2020 Multi-Employer Pension Contribution, the 2020 OG&A Adjusted Items, the COVID-19 Investments, growth in our digital channel as a result of heightened demand during the pandemic, increased incentive plan costs and the effect of decreased fuel sales, which increases our OG&A rate, as a percentage of sales, partially offset by the effect of increased sales due to the pandemic which decreases our OG&A rate, as a percentage of sales, the 2019 OG&A Adjusted Items and broad based improvement of Restock Kroger cost savings initiatives that drive administrative efficiencies, store productivity and sourcing cost reductions.
Excluding the effect of fuel, the 2020 OG&A Adjusted Items and the 2019 OG&A Adjusted Items, our OG&A rate decreased 6 basis points in the first three quarters of 2020, compared to the first three quarters of 2019. This decrease resulted primarily from the effect of increased sales due to the pandemic which decreases our OG&A rate, as a percentage of sales and broad based improvement of Restock Kroger cost savings initiatives that drive administrative efficiencies, store productivity and sourcing cost reductions, partially offset by the 2020 Multi-Employer Pension Contribution, the COVID-19 Investments, growth in our digital channel as a result of heightened demand during the pandemic and increased incentive plan costs. Excluding the effect of fuel, the 2020 OG&A Adjusted Items, the 2019 OG&A Adjusted Items and the 2020 Multi-Employer Pension Contribution, our OG&A rate improved 31 basis points.
Rent Expense
Rent expense decreased, as a percentage of sales, in both the third quarter and first three quarters of 2020, compared to the same periods in 2019. This decrease resulted primarily from the effect of increased sales due to the pandemic which decreases our rent expense, as a percentage of sales.