The Company. We are an internally managed and self-advised real estate investment trust, or REIT, primarily engaged in the ownership and operation of office buildings in the United States. We were formed in 1986 under Maryland law and we have elected to be taxed as a REIT under the Internal Revenue Code of 1986, as amended (the Code). The Company operates as what is commonly referred to as an umbrella partnership real estate investment trust, or UPREIT, conducting substantially all of its activities through EQC Operating Trust, a Maryland real estate investment trust (the Operating Trust).
The Company beneficially owned 99.96% of the outstanding shares of beneficial interest, designated as units, in the Operating Trust (OP Units) as of December 31, 2018, and the Company is the sole trustee of the Operating Trust. As the sole trustee, the Company generally has the power under the declaration of trust of the Operating Trust to manage and conduct the business of the Operating Trust, subject to certain limited approval and voting rights of other holders of OP Units.
At December 31, 2018, our portfolio consisted of 10 properties, with a total of 5.1 million square feet. Over the past five years, we disposed of 158 properties and three land parcels totaling 40.7 million square feet for an aggregate gross sales price of $5.4 billion, as well as $704.8 million of common shares of Select Income REIT. The remaining 10 properties were 94.8% leased and had 91.2% commenced occupancy as of December 31, 2018. In 2018, the Company completed seven property dispositions totaling $1.0 billion. In addition, in January 2019, the Company entered into an agreement to sell the entity owning 1735 Market Street in Philadelphia for a gross sale price of $451.6 million. We currently have two other properties totaling 1.4 million square feet for sale.