diff --git a/arc/main.py b/arc/main.py
index 1b52a8bff1..9229764dc8 100644
--- a/arc/main.py
+++ b/arc/main.py
@@ -19,7 +19,8 @@
 from rmgpy.reaction import Reaction
 
 import arc.rmgdb as rmgdb
-from arc.settings import arc_path, default_levels_of_theory, check_status_command, servers, valid_chars
+from arc.settings import arc_path, default_levels_of_theory, check_status_command, servers, valid_chars,\
+    ess_settings
 from arc.scheduler import Scheduler
 from arc.arc_exceptions import InputError, SettingsError, SpeciesError
 from arc.species.species import ARCSpecies
@@ -83,9 +84,9 @@ class ARC(object):
     def __init__(self, input_dict=None, project=None, arc_species_list=None, arc_rxn_list=None, level_of_theory='',
                  conformer_level='', composite_method='', opt_level='', freq_level='', sp_level='', scan_level='',
                  ts_guess_level='', fine=True, generate_conformers=True, scan_rotors=True, use_bac=True,
-                 model_chemistry='', ess_settings=None, initial_trsh=None, t_min=None, t_max=None, t_count=None,
+                 model_chemistry='', initial_trsh=None, t_min=None, t_max=None, t_count=None, run_orbitals=True,
                  verbose=logging.INFO, project_directory=None, max_job_time=120, allow_nonisomorphic_2d=False,
-                 job_memory=1500, run_orbitals=True):
+                 job_memory=1500):
 
         self.__version__ = '1.0.0'
         self.verbose = verbose
@@ -324,7 +325,7 @@ def __init__(self, input_dict=None, project=None, arc_species_list=None, arc_rxn
             project_directory = project_directory if project_directory is not None\
                 else os.path.abspath(os.path.dirname(input_dict))
             self.from_dict(input_dict=input_dict, project=project, project_directory=project_directory)
-        if self.ess_settings is None:
+        if self.ess_settings is None or self.ess_settings = dict():
             self.determine_ess()
         self.restart_dict = self.as_dict()
         self.determine_model_chemistry()
@@ -892,9 +893,10 @@ def determine_ess(self, diagnostics=False):
                 if g03 or g09 or g16:
                     if diagnostics:
                         logging.info('Found Gaussian on {3}: g03={0}, g09={1}, g16={2}'.format(g03, g09, g16, server))
-                    if self.ess_settings['gaussian'] is None or 'precedence' in servers[server]\
-                            and servers[server]['precedence'] == 'gaussian':
-                        self.ess_settings['gaussian'] = server
+                    if 'gaussian' not in self.ess_settings.keys():
+                        self.ess_settings['gaussian'] = [server]
+                    else:
+                        self.ess_settings['gaussian'].append(server)
                 elif diagnostics:
                     logging.info('Did NOT find Gaussian on {3}: g03={0}, g09={1}, g16={2}'.format(g03, g09, g16, server))
                 cmd = '. ~/.bashrc; which qchem'
@@ -902,9 +904,10 @@ def determine_ess(self, diagnostics=False):
                 if qchem:
                     if diagnostics:
                         logging.info('Found QChem on {0}'.format(server))
-                    if self.ess_settings['qchem'] is None or 'precedence' in servers[server]\
-                            and servers[server]['precedence'] == 'qchem':
-                        self.ess_settings['qchem'] = server
+                    if 'qchem' not in self.ess_settings.keys():
+                        self.ess_settings['qchem'] = [server]
+                    else:
+                        self.ess_settings['qchem'].append(server)
                 elif diagnostics:
                     logging.info('Did NOT find QChem on {0}'.format(server))
                 cmd = '. .bashrc; which molpro'
@@ -912,9 +915,10 @@ def determine_ess(self, diagnostics=False):
                 if molpro:
                     if diagnostics:
                         logging.info('Found Molpro on {0}'.format(server))
-                    if self.ess_settings['molpro'] is None or 'precedence' in servers[server]\
-                            and servers[server]['precedence'] == 'molpro':
-                        self.ess_settings['molpro'] = server
+                    if 'molpro' not in self.ess_settings.keys():
+                        self.ess_settings['molpro'] = [server]
+                    else:
+                        self.ess_settings['molpro'].append(server)
                 elif diagnostics:
                     logging.info('Did NOT find Molpro on {0}'.format(server))
             if diagnostics:
@@ -926,8 +930,8 @@ def determine_ess(self, diagnostics=False):
             if self.ess_settings['molpro']:
                 logging.info('Using Molpro on {0}'.format(self.ess_settings['molpro']))
             logging.info('\n')
-        if not self.ess_settings['gaussian'] and not self.ess_settings['qchem'] and not self.ess_settings['molpro']\
-                and not diagnostics:
+        if 'gaussian' not in self.ess_settings[] and 'qchem' not in self.ess_settings[]\
+                and 'molpro' not in self.ess_settings[] and not diagnostics:
             raise SettingsError('Could not find any ESS. Check your .bashrc definitions on the server.\n'
                                 'Alternatively, you could pass a software-server dictionary to arc as `ess_settings`')
         elif diagnostics:
diff --git a/arc/settings.py b/arc/settings.py
index a7e9331d68..dd20cc6189 100644
--- a/arc/settings.py
+++ b/arc/settings.py
@@ -34,7 +34,6 @@
         'address': 'server1.host.edu',
         'un': '<username>',
         'key': 'path_to_rsa_key',
-        'precedence': 'molpro',
     },
     'server2': {
         'cluster_soft': 'Slurm',  # Simple Linux Utility for Resource Management
@@ -45,6 +44,15 @@
     }
 }
 
+# List here servers you'd like to associate with specific ESS.
+# An ordered list of servers indicates priority
+# Keeping this dictionary empty will cause ARC to scan for software on the servers defined above
+ess_settings = {
+    'gaussian': ['server1', 'server2'],
+    'molpro': 'server2',
+    'qchem': 'server1',
+}
+
 # List here (complete or partial) phrases of methods or basis sets you'd like to associate to specific ESS
 # Avoid ascribing the same phrase to more than one server, this may cause undeterministic assignment of software
 # Format is levels_ess = {ess: ['phrase1', 'phrase2'], ess2: ['phrase3', 'phrase3']}