Third-party logistics (3PL) providers will take a larger share of U.S. transportation and logistics spending in 2014, according to a forecast from Armstrong & Associates Inc., a consultancy.

The Armstrong data, which appeared today in a research note published by investment firm Morgan Stanley & Co., projected that 3PL gross revenues, as a percentage of total logistics costs, will approach 11.2 percent this year. For 2013, the percentage is expected to come in at around 10.8 percent. The 2013 data has not been finalized. Gross 3PL revenues are sales before factoring in the cost of purchased transportation. Third-party providers generally do not own transport assets and rely on others to move their customers' freight.

William Greene, Morgan Stanley's lead transport analyst, said in the note that Armstrong data indicates 3PL revenues will grow at a significantly faster rate than U.S. gross domestic product (GDP) "for the foreseeable future."

U.S. logistics costs reached $1.39 trillion in 2013, according to the Council of Supply Chain Management Professionals' "State of Logistics Report," sponsored by Penske Logistics, which was released in mid-June.

For nearly two decades, 3PL growth has far exceeded that of GDP. Armstrong, which specializes in the 3PL category, said late last year that domestic 3PL revenue grew at a 10-percent compounded annual rate since 1996. From 1996 to 2013, only once—in recession-wracked 2009—did the domestic sector report year-over-year declines in revenue, according to the firm.

3PLs have benefited as companies of all sizes continue to outsource domestic and international logistics services to specialists who can execute increasingly complex functions more cost-effectively than their customers.

However, a growing top line may not translate into heightened profitability. The proliferation of new technologies and increasing competition among 3PLs could result in continued margin pressures in the years ahead, Greene wrote.

In a recent shipper survey, Morgan Stanley found that 37 percent of respondents used six or more brokers in June, compared with 30 percent two years prior. The data showed that shippers are relying more on brokers to move their goods and that the typical respondent is doling out its spend to a larger number of intermediaries.