Main Street Capital provided an update of its portfolio investment activity for the fourth quarter of 2011. Main Street said it completed lower middle market (LMM) portfolio investments totaling $42.7 million in five previously announced new portfolio companies.

Main Street’s new LMM portfolio investments included investments in the following companies:

RMB and Gault Financial – $10.5 million investment in first lien secured debt with equity warrant participation; the company is a healthcare revenue cycle management company serving customers nationwide.

Radial Drilling Services – $4.2 million investment in first lien secured debt with equity warrant participation; the company is a provider of patented technologies, equipment and personnel to increase production in mature oil and gas wells using radial drilling through modified coiled tubing technology.

SAMBA Holdings – $4.0 million investment, consisting of $3.0 million in first lien secured debt and $1.0 million in direct equity; the company is a provider of fleet compliance software and services to car and truck fleet owners.

Willis Group – $9.0 million investment in first lien secured debt; the company is a provider of staffing and recruitment services through three specialized brands.

NRP Jones – $15.0 million investment, consisting of $12.1 million in first lien secured debt and $2.9 million in direct equity; the company manufactures hydraulic, industrial, and oilfield hoses, fittings and assemblies for both original equipment manufacturers and hose and fitting distributors.

In addition to the LMM portfolio investment activity discussed above, Main Street said it completed private placement portfolio investments totaling $35.1 million during the fourth quarter of 2011, including investments in eight new companies with a weighted average effective yield of approximately 11.4%.