The MBTA's unsustainable operating budget is hamstrung by "stagnating" revenues, costs that are growing at twice the rate of inflation, and a fleet that is the oldest among its peer transit systems, according to details of a draft task force report.

Baker administration officials released portions of the draft ahead of this week's expected full public release of a final report examining the MBTA. Gov. Charlie Baker formed the task force in the wake of this winter's widespread T service failures.

Baker has emphasized management and cost controls as means towards stabilizing the MBTA and improving performance, while others say system problems are best addressed by new revenues. The Legislature in recent years has tried both reform and revenue approaches.

The draft points to "limited cost control, low labor productivity, and high maintenance costs" associated with equipment, including Red Line railcars built in 1969.

On the revenue side, the draft notes ridership is "unevenly measured and receives insufficient emphasis as a means of increasing fare revenue." Between 2001 and 2015, MBTA revenues grew by only 2.12 percent per year, the draft says, and the percentage of operating expenses, excluding debt service, is 39 percent, below peer systems.

MBTA fare receipts cover a significantly lower percentage of overall costs than peer systems in New Jersey, San Francisco, London and other metro areas, according to the draft.

Task force member Jane Garvey told The Boston Globe Monday that management and operational practices at the T "really need to be put in place first and foremost." Garvey said, "We certainly acknowledge that chronic underinvestment has been an issue, but we need to right the ship first."

An administration official declined to say whether the report will call on the Legislature to invest more money in the MBTA, noting recommendations will be made public later this week.