drilled wells, which has impaired the recoverability of the assets as they approach the end of their useful lives. The carrying values of the long-lived assets related to our natural gas interests were $2.0 million as of December 31, 2020.
Revenues increased 1.5% in 2020 compared to 2019. Revenues from our Lime and Limestone Operations increased 1.7% in 2020, compared to 2019, primarily due to the addition of limestone sales by Carthage to agriculture and roofing customers, and increased sales to the Company’s construction customers, partially offset by decreased demand from the Company’s oil and gas services, environmental and steel customers. Revenues in 2020 were also favorably impacted by an increase in average selling prices for our lime and limestone products of 3.6%.
Gross profit increased 14.2% in 2020 compared to 2019. Gross profit from our Lime and Limestone Operations in 2020 increased 14.1%, compared to 2019, primarily due to increases in the average selling prices for our lime and limestone products, lower fuel costs, and increased operating efficiencies associated, in part, with our new, fuel-efficient kiln at our St. Clair facility, which began producing commercially saleable quicklime in the second quarter 2019, partially offset by increased costs incurred in 2020 associated with responding to the COVID-19 pandemic.
Interest expense remained flat at $0.2 million for each of 2020 and 2019. Interest and other income, net, decreased $1.4 million in 2020, or 76.2%, compared to 2019, primarily due to decreased interest rates received on our cash and cash equivalents balances in 2020.
Net income increased $2.2 million, or 8.3%, in 2020, compared to 2019. Net income per fully diluted share increased to $5.00 in 2020, compared to $4.64 in 2019. Cash flows from operations enabled us to make $17.1 million of capital investments, including our acquisition of Carthage for $8.4 million. It also enabled us to pay $3.6 million in dividends and increase our cash balances to $83.6 million as of December 31, 2020, compared to $54.3 million as of December 31, 2019. As of December 31, 2020, we had no debt outstanding.
On January 29, 2021, we announced that our Board of Directors had declared a regular quarterly cash dividend of $0.16 (16 cents) per share. The dividend is payable on March 12, 2021 to shareholders of record on February 19, 2021.
Absent a significant acquisition opportunity arising during 2021, we anticipate funding our operating and capital needs and our quarterly cash dividend from our cash balances on hand and cash flows from operations.
Lime and Limestone Operations.
In our Lime and Limestone Operations, we produce and sell PLS, aggregate, quicklime, hydrated lime and lime slurry. The principal factors affecting our success are the level of demand and prices for our products and whether we are able to maintain sufficient production levels and product quality while controlling costs.
Inclement weather conditions, such as winter ice and snow storms, cold weather, hurricanes, tornadoes and excessive rainfalls generally reduce the demand for lime and limestone products supplied to construction-related customers that account for a significant amount of our revenues. Inclement weather also interferes with our open-pit mining operations and can disrupt our plant production. In addition to weather, various maintenance, environmental, accident and other operational and construction issues can also disrupt our operations and increase our operating expenses.
Demand for our products in our market areas is also affected by general economic conditions, the pace of construction, the demand for steel, the level of oil and gas drilling in our markets, the level of governmental and private funding for highway construction and infrastructure and utility plant usage of coal for power generation. Demand for our lime and limestone products from our construction customers increased in 2020. However, demand for our lime and limestone products from our oil and gas services, environmental and steel customers decreased. Oil prices declined sharply in 2020 compared to 2019, which resulted in a curtailment of drilling activities during 2020 and lower demand from our oil and gas services customers.
The emergence of COVID-19 in the United States in the first quarter 2020 created significant volatility, uncertainty and economic disruption to the general business environment. Federal, state, and local governmental responses to the COVID-19 pandemic, which include restrictions requiring social distancing and restrictions on business activities and movement of people in the markets for our lime and limestone products, began to take effect the last two