MPLX LP (MPLX) is the K-1-issuing master limited partnership, "MLP," child of Marathon Petroleum (MPC). Now that MPC merged its two children, MPLX and Andeavor Logistics (ANDX), the surviving entity MPLX represents a significant amount of gathering, processing, pipeline, logistics, and storage energy assets spread across the US.
Source: Company presentation
At $25 billion in market cap, MPLX is neither small nor concentrated. As such, it is probably more comparable to large-cap midstream entities Enterprise Products Partners (EPD), Williams (WMB), or Energy Transfer (ET) rather than smaller, more localized firms such as EQM Midstream