Electric energy networks provide the energy necessary to carry out daily operations in education, health care, commerce, entertainment, defense, and government. Smart grids (SG) have been proposed as a mechanism to modernize and facilitate the operation of energy grids in the presence of multiple third-parties vying to sell electricity and related services. Recently, a new concept has emerged in relation with SG: transactive energy – a framework to integrate and coordinate multiple independent suppliers of electric services in an economic marketplace that enables purchases in a way that obeys the physical constrains of the underlying energy grid. Our team is developing a transactive energy framework called Open Access Smart Grids (OASIS). OASIS features a distribution-level marketplace where the underlying electric resources and services are open to access and provisioned by third parties. In this paper, we present a cloudbased and big data-enabled brokerage system for Smart grids, which is a critical component of OASIS. In this brokerage system, consumer energy requests, and energy bids issued by producers, are collected and matched to find a list of energy purchase orders to be dispatched to the winning producers. A central piece in the system is an energy broker software agent, which drives the bidding process.