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An experimental study of the electrical transport phenomena in magnetic fields H up to 15 T in pressed samples of a porous system composed of single-walled carbon nanotubes in the temperature range 1.39 K <T<300 K is reported. Below 60 K, the exp[1/T1/4] temperature dependence of the direct current electrical resistance R(T,0) is found. Low-field transverse magnetoresistance (MR), [R(T,H)−R(T,0)]/R(T,0), below 60 K is negative and is discussed in terms of a quantum interference effect on a three-dimensional variable range hopping (3D–VRH) mechanism. Based on the results of R(T,0) and MR, we propose 3D–VRH conduction within the nanotube bundles (intrabundle hopping) or between the nanotube bundles (interbundle hopping) through their contacts.