diff --git a/packages/access-mocsy/package.py b/packages/access-mocsy/package.py
new file mode 100644
index 0000000..5da84fd
--- /dev/null
+++ b/packages/access-mocsy/package.py
@@ -0,0 +1,108 @@
+# Copyright 2013-2024 Lawrence Livermore National Security, LLC and other
+# Spack Project Developers. See the top-level COPYRIGHT file for details.
+#
+# Copyright 2024 ACCESS-NRI
+#
+# SPDX-License-Identifier: (Apache-2.0 OR MIT)
+
+from spack.package import find_libraries, install, join_path, mkdirp
+
+# https://spack.readthedocs.io/en/latest/build_systems/makefilepackage.html
+class AccessMocsy(MakefilePackage):
+    """Routines to model ocean carbonate system thermodynamics. ACCESS NRI's fork."""
+
+    homepage = "https://www.access-nri.org.au"
+    git = "https://github.com/ACCESS-NRI/mocsy.git"
+
+    maintainers("harshula")
+
+    version("master", branch="master")
+    version("mom5", branch="mom5", preferred=True)
+
+    # Need: self.spec["mpi"].mpifc
+    depends_on("mpi")
+
+    _header = join_path("src", "mocsy_DNADHeaders.h")
+    _libname = "libmocsy.a"
+    _pcfile = "mocsy.pc"
+    _pkgdir = "pkgconfig"
+    _modfiles = [
+        "dual_num_auto_diff.mod",
+        "mocsy_buffesm.mod",
+        "mocsy_constants.mod",
+        "mocsy_depth2press.mod",
+        "mocsy_derivauto.mod",
+        "mocsy_derivnum.mod",
+        "mocsy_errors.mod",
+        "mocsy_f2pco2.mod",
+        "mocsy_gasx.mod",
+        "mocsy_p2fco2.mod",
+        "mocsy_p80.mod",
+        "mocsy_phsolvers.mod",
+        "mocsy_rho.mod",
+        "mocsy_rhoinsitu.mod",
+        "mocsy_singledouble.mod",
+        "mocsy_sw_adtg.mod",
+        "mocsy_sw_ptmp.mod",
+        "mocsy_sw_temp.mod",
+        "mocsy_tis.mod",
+        "mocsy_tpot.mod",
+        "mocsy_vars.mod",
+        "mocsy_varsolver.mod",
+    ]
+
+    def url_for_version(self, version):
+        return "https://github.com/ACCESS-NRI/mocsy/tarball/{0}".format(version)
+
+    @property
+    def libs(self):
+        return find_libraries(
+            "libmocsy", root=self.prefix, shared=False, recursive=True
+        )
+
+    def _create_pkgconf(self, spec, prefix):
+
+        text = f"""\
+prefix={prefix}
+exec_prefix=${{prefix}}
+libdir=${{exec_prefix}}/lib
+includedir=${{prefix}}/include
+
+Name: mocsy
+Description: Routines to model ocean carbonate system thermodynamics.
+Version: 2024.08.1
+Libs: -L${{libdir}} -lmocsy
+Cflags: -I${{includedir}}
+Fflags: -I${{includedir}}
+"""
+
+        with open(join_path(self.stage.source_path, self._pcfile), "w", encoding="utf-8") as pc:
+            nchars_written = pc.write(text)
+
+        if nchars_written < len(text):
+            raise OSError
+
+    def build(self, spec, prefix):
+        build = Executable("make")
+        build(
+            self._libname,
+            "FC=" + self.spec["mpi"].mpifc,
+            # Copied from MOM5/bin/mkmf.template.nci
+            "FCFLAGS=-fno-alias -safe-cray-ptr -fpe0 -ftz -assume byterecl -i4 -r8 -traceback -nowarn -check noarg_temp_created -assume nobuffered_io -convert big_endian -grecord-gcc-switches -align all -g3 -O2 -xCORE-AVX2 -debug all -check none",
+            "F90=" + self.spec["mpi"].mpifc
+        )
+        self._create_pkgconf(spec, prefix)
+
+    def install(self, spec, prefix):
+
+        # Creates prefix.lib too
+        pkgconfdir = join_path(prefix.lib, self._pkgdir)
+        mkdirp(pkgconfdir)
+        mkdirp(prefix.include)
+
+        install(join_path(self.stage.source_path, self._libname), prefix.lib)
+        install(join_path(self.stage.source_path, self._header), prefix.include)
+        for f in self._modfiles:
+            install(join_path(self.stage.source_path, f), prefix.include)
+        install(join_path(self.stage.source_path, self._pcfile), pkgconfdir)
+