did not provide additional tenant rent abatements, however, we did provide lease deferrals of $0.1 million due to the impact of the COVID-19 pandemic.
During the three months ended September 30, 2020, we had seven commercial and rural real estate sales totaling approximately 232 acres for $2.2 million, resulting in a gross profit margin of approximately 63.6%. During the three months ended September 30, 2019, we had six commercial and rural real estate sales totaling approximately 56 acres for $2.2 million, resulting in a gross profit margin of approximately 90.9%.
Timber revenue increased by $0.3 million during the three months ended September 30, 2020, as compared to the same period in 2019. The increase is primarily due to an increase in sales of fill dirt and other products. There were 84,000 tons sold during the three months ended September 30, 2020, as compared to 82,000 tons sold during the same period in 2019. The average price per ton sold decreased to $14.99 during the three months ended September 30, 2020, as compared to $15.16 during the same period in 2019. Timber gross margin increased during the three months ended September 30, 2020, to 87.5% as compared to 84.6% during the same period in 2019, primarily due an increase in sales of fill dirt and other products. The cost of timber revenue is primarily fixed, which also resulted in an increase to gross margin for the period.
Other operating expenses include salaries and benefits, property taxes, CDD assessments, professional fees, marketing, project administration and other administrative expenses.
The increase of $0.4 million in depreciation, amortization and depletion expense during the three months ended September 30, 2020, as compared to the same period in 2019, was primarily due to new properties placed in service.
Interest expense primarily includes interest incurred from our commercial leasing project financing and CDD debt.
Other income, net for the three months ended September 30, 2019 includes a gain of $0.8 million on land contributed to our unconsolidated Busy Bee JV. See Note 4. Joint Ventures for additional information. The three months ended September 30, 2019, also included a $0.9 million gain on insurance recovery for the Pier Park Crossings JV related to Hurricane Michael. See Note 7. Hurricane Michael for additional information.
Nine Months Ended September 30, 2020 compared to the Nine Months Ended September 30, 2019
Total leasing revenue increased $3.0 million, or 27.0%, during the nine months ended September 30, 2020, as compared to the same period in 2019. This increase is primarily due to new leases at Pier Park Crossings apartments, which began leasing in the second quarter of 2019, as well as other new leases and higher rental rates. Cost of leasing revenue during the nine months ended September 30, 2020 includes $0.7 million of business interruption insurance proceeds received for Pier Park Crossings apartments related to Hurricane Michael. Leasing gross margin increased during the nine months ended September 30, 2020 to 71.6%, as compared to 69.4% during the same period in 2019. Excluding the business interruption proceeds received during the nine months ended September 30, 2020, our leasing gross margin was 66.7% during the nine months ended September 30, 2020, as compared to 69.4% during the same period in 2019. As of September 30, 2020, we had net rentable square feet of approximately 904,000, of which approximately 758,000 square feet was under lease. As of September 30, 2019, we had net rentable square feet of approximately 822,000, of which approximately 757,000 square feet was under lease. During the nine months ended September 30, 2020 we provided tenant rent abatements totaling $0.1 million, along with lease deferrals of $0.4 million due to the impact of the COVID-19 pandemic.
The diversity of our commercial segment complements the growth of our communities and our residential and hospitality segments. Commercial and rural real estate revenue can vary depending on the proximity to developed areas and the mix and characteristics of commercial and rural real estate sold in each period, with varying compositions of retail, office, industrial and other commercial uses. During the nine months ended September 30, 2020, we had nineteen commercial and rural real estate sales totaling approximately 433 acres for $7.2 million, resulting in a gross profit margin of approximately 69.4%. Commercial and rural real estate revenue for the nine months ended September 30, 2020 included $1.8 million related to the sale of the SouthWood Town Center. During the nine months ended September 30, 2019, we had fifteen commercial and rural real estate sales totaling approximately 161 acres for