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 OG&A Adjusted Items and the 2019 OG&A Adjusted Items, our OG&A rate decreased 6 basis points in 2020, compared to 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 from cost savings initiatives that drive administrative efficiencies, store productivity and sourcing cost reductions, partially offset by the First Quarter 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 $236 million First Quarter 2020 Multi-Employer Pension Contribution from the above calculation, which we proactively made to cover future funding requirements for certain multi-employer pension plans, our OG&A rate improved 25 basis points.
Rent Expense
Rent expense was $874 million, or 0.66% of sales, for 2020, compared to $884 million, or 0.72% of sales, for 2019. Rent expense, as a percentage of sales, decreased 6 basis points in 2020, compared to 2019, primarily due to the effect of increased sales due to the pandemic which decreases our rent expense, as a percentage of sales.
Depreciation and Amortization Expense
Depreciation and amortization expense was $2.7 billion, or 2.07% of sales, for 2020, compared to $2.6 billion, or 2.17% of sales, for 2019. Depreciation and amortization expense, as a percentage of sales, decreased 10 basis points in 2020, compared to 2019. This decrease resulted primarily from the effect of increased sales due to the pandemic which decreases our depreciation expense, as a percentage of sales, partially offset by decreased fuel sales, which increases our depreciation expense, as a percentage of sales, additional depreciation on capital investments, excluding mergers and lease buyouts, of $3.2 billion during 2020 and a decrease in the average useful life on these capital investments. Our strategy includes initiatives to enhance the customer experience in stores, improve our process efficiency and integrate our digital shopping experience through technology developments. As such, the percentage of capital investments related to digital and technology has grown compared to the prior year, which has caused a decrease in the average depreciable life of our capital portfolio.
Operating Profit and FIFO Operating Profit
Operating profit was $2.8 billion, or 2.10% of sales, for 2020, compared to $2.3 billion, or 1.84% of sales, for 2019. Operating profit, as a percentage of sales, increased 26 basis points in 2020, compared to 2019, due to improved sales to retail customers without fuel, a higher gross margin rate, decreased rent and depreciation and amortization expenses, as a percentage of sales, and increased fuel earnings, partially offset by increased OG&A expense with fuel, as a percentage of sales.
FIFO operating profit was $2.8 billion, or 2.09% of sales, for 2020, compared to $2.4 billion, or 1.93% of sales, for 2019. FIFO operating profit, excluding the 2020 and 2019 Adjusted Items, increased 64 basis points in 2020, compared to 2019, due to improved sales to retail customers without fuel, a higher gross margin rate, decreased rent and depreciation and amortization expenses, as a percentage of sales, and increased fuel earnings, partially offset by increased OG&A expense with fuel, as a percentage of sales.
Specific factors contributing to the trends driving operating profit and FIFO operating profit identified above are discussed earlier in this section.